minute, compared with the whole bulk of the animal, as to appear quite rudimentary. The simple lateral uncini, moreover, are only distinctly visible towards the posterior extremity of the sac. Both these genera seem to be more intimately related to Murex and its congeners than to the Buccinidæ.

Triphoris is now, as it would appear from the characters of its shell alone, placed with Cerithium, but the comparison of the internal anatomy of those genera offers no countenance to their supposed affinity; thus, single spherical otolithes occupy the auditory sacs of Triphoris, while those of Cerithium contain otoconia. The proboscis of the former is long and retractile. The lingual membrane of Triphoris besides, though long and ribbon-like, supports a multiserial pavement of minute teeth, while that of Cerithium is septiserial, resembling in many particulars the tongue-strap of Pupina and allied forms.

The Columbellæ deserve to be elevated to the rank of a family, distinguished from the Buccinide by the unarmed rachis, and curved versatile pleural teeth of the tongue-strap.

Although not fully satisfied of the propriety of separating the genus Conidea from Columbella, the author thinks there can be no doubt that Pusiostoma, formerly placed with the Columbellæ, distinct genus clearly referable to the Buccinidæ.

forms a very

As great difference of opinion has always existed as to the distribution of the sexes amongst Gasteropods, so far the author is unable to vouch for the whole truth of the arrangement above given, but he thinks that if there is anything incongruous in it, the correction of errors in that particular would seem to be most likely to restore harmory and support the truth of the system.

In the course of his inquiries the author was impressed with the fact, that various genera of terrestrial gasteropods, which agree with each other as far as regards their respiratory organs and mode of respiration, differ essentially in their general organization, whereas they are in this respect severally related to fluviatile and marine genera, which are obviously constructed on the same anatomical type.

In this way a terrestrial genus, having few structural points of agreement to connect it laterally, as it were, with others of the same habit, forms a member of a beautifully connected natural series, traceable from it through fluviatile and littoral forms to others which are altogether marine.

As an example of these relations the following Table is given, and it might have been extended and rendered more complete, had the author not preferred to limit it to such cases as have come under his own examination.

Sexes combined.

Otoconia.

Pavement.

Teeth nume

Rachis and Rachis unise- Rachis unise

rous, uniform Pleuræ multi- rial, Pleuræ rial, Pleura

This Table shows the natural affinities of four principal divisions of terrestrial gasteropods, proceeding, as it were, in parallel lines, without any very obvious lateral connexions, through fluviatile and littoral forms, conducting to certain marine genera distinguished by this alliance from all others having no terrestrial representatives, and being therefore more restrictedly marine. It may be remarked that the importance of the characters placed at the head of the Table has been proved by the comparison of other anatomical particulars in those genera, and so far their efficiency in other cases is substantiated.

The author adds the following observations on the anatomy of the Siphonaria and Amphibola, as bearing on their position in the first series of the foregoing Table :

"Siphonaria appears to enjoy the power of breathing in both air and water with equal facility, and on examination, we find the respiratory surface so constituted as to afford a ready explanation of the fact. Thus, in connexion with a narrow, combed, or rather transversely plaited gill, numerous vessels ramify extensively, and

anastomose freely upon the roof of the respiratory chamber. The mouth is armed with lateral labial plates, and the lingual dentition is not unlike that of Amphibola, to which genus it is further related by the absence of tentacula, and the general configuration of its head.

"Amphibola exhibits a close relationship to the Pulmonifera in many essential anatomical points, but it has a veritable combed gill, which, arising from a deep recess on the left side of the branchial chamber, and thence passing obliquely forwards towards the right side, terminates in a pointed extremity, in front of which there is a small glandular body, probably a renal organ. The margin of the mantle may be traced continuously round the neck and the base of the foot, being attached in its entire extent, with the exception of a small portion which arches over a narrow respiratory opening on the right side of the nape. The lingual sac is small, like a cæcal process appended to the antero-inferior part of the oesophagus. The dental organs present a pavement of narrow basal plates with very long and gently curved cusps. The teeth of the central series are much larger than the rest, and exhibit a remarkable conformation; thus a rounded process projects in the middle and several minute denticulations arm its base on either side. I have not succeeded in detecting either lingual cartilages or labial plates in my spirit-preserved specimens, and but for the support furnished by analogy, I would incline to the belief that they are absent in the present case.

"The remark made by Mr. Woodward in his very valuable little work the Manual of Mollusca,' that the anomalous genus Amphibola has an unusually broad tongue armed with teeth similar to those of the snail, is not quite correct. The misconception most probably originated in the inspection of a preparation belonging to Mr. Wilton of Gloucester, and from which Mr. Woodward's figure has been taken, as 'part of the tongue of Amphibola avellana;' but having myself dissected several specimens of this very species obtained at New Zealand, I am satisfied that Mr. Wilton's preparation has been by some accident improperly named.

"The general scheme of the generative system in Amphibola corresponds very closely with that of Helix, Bulimus and such Pulmonifera. The ovarium is imbedded in the liver near the summit of its spiral turns, and a small convoluted oviduct leads downwards and forwards along its inner or concave side. The testis lies con

siderably in advance of the ovary; the intromittent organ forms a prominence in the floor of the respiratory chamber, and finally the generative orifices open on the right side."

II. "On the Sea Saw-dust of the Pacific." By JOHN DENIS MACDONALD, Esq., Assistant Surgeon R.N. Communicated by Captain DENHAM, R.N., F.R.S. Received January 13, 1857.

(Abstract.)

In this communication the author gives a description (illustrated by figures) of the remarkable little algal so frequently met with in the South Pacific, scattered over the surface of the water in broad streaks and patches of a pale yellowish-brown tint, and which is known under the name of "Sea Saw-dust."

After adverting to the occurrence of a similar phenomenon in other parts of the globe, and citing the account given of the Trichodesmium erythræum of the Red Sea by MM. Evernor Dupont and Montagne, together with a description extracted from the Colombo Herald' of May 14, 1844, of what was obviously an example of a vegetable scum of the same kind occurring on the sea off Ceylon, the author remarks, that in the instances met with by himself he did not recognize the fœtid odour so generally and pointedly spoken of in the accounts of others. He then states results of his own observation as follows:

"It was rather difficult at first to determine whether our species is to be referred to the Oscillatoridæ or the Confervidæ. In the latter, a linear series of tubular cells compose the filaments, which are thus said to be jointed, but in the former, although the filaments are tubular, simple and continuous without actual joints, a pseudo-jointed appearance is presented by the apposition of the little masses of contained colouring matter. Notwithstanding, having submitted the 'sea saw-dust' of the Pacific to microscopic examination on several occasions, I was much inclined to believe that the filaments were actually jointed; and this view is supported by the cir

cumstance that an empty tubule, or one in which the parietes may be traced continuously without being interrupted by joints or internal septa, has never fallen under our notice; besides which the filaments are exceedingly brittle, usually suffering cleavage in the transverse direction. It, however, undoubtedly belongs to the Oscillatorida.

"When the filaments are first removed from the water, they may be observed adhering side by side in little bundles or fasciculi; and besides the colouring matter, the little cells, or at least the intervals between the septa, contain globules of air, which sufficiently account for their buoyancy; and, moreover, in this respect, although their abiding place is the open ocean, their habit can scarcely be regarded as very different from that of those species which flourish in damp localities exposed to the atmosphere.

"The filaments are all very short compared with their diameter, with rounded extremities; and when immersed some little time in fluid so that the contained air-bubbles make their escape or are taken up, the pale colouring matter appears to fill the cells completely, and a central portion, a little darker than the rest, may be distinctly perceived in each compartment intersected by a very delicate transverse partition.

"We have found this species off the coast of Australia and in Moreton Bay, amongst the Polynesian Islands, and on two separate occasions off the Loyalty Group, in nearly the same geographical position."