344 MOLLUSCA.’ 
Mollusca. differ greatly from one another and from the generic char- 
have been transferred by late authors. But improvements Mollusea. 
=e acter. Some are found recent on our shores, while others 
of a more important kind have been effected. Linneeus had ex 
occur only in a fossil state. Lamark, haying rectified the 
Linnzan character of the genus, has separated many species, 
now grouped, into distinet genera. In the restricted genus 
Anomia, the under valye has a hole or grooye near the 
beak, which is closed by a testaceous operculum. This ap- 
pendage is fixed to rocks or stones, and has a ligament ‘at- 
tached to it. 
In the genus Cranta, represented by the Anomia erano- 
laris of Linnzus, the under valve is pierced by three holes, 
which are oblique and unequal. The genus GryPH=zA was 
constituted from the Anomia Gryphus of Linnzus. The 
inferior valve is concave, terminating in a spirally involuted 
beak, projecting upwards ; the upper valve is small, and re- 
sembles a lid. A transversely striated pit at the hinge con- 
tains the ligament. The only recent species known is called 
G. angulata. Many species are found in a fossil, state in 
the rocks of this country. 
Among the Anomia, Linneus placed the shells which 
compose the genus TrreBratuLa, the characters of which 
are so obvious and distinct. In this genus, which is inequi- 
valve and regular, the beak of the larger valve is produced, 
and pierced with a hole, through which the ligament of ad- 
hesion passes. From the great extent of this genus in fossil 
species, several subdivisions have been proposed. 
From the Anomia placenta of Linnzeus, Lamark has form- 
ed his genus Puacuna. ‘The hinge is remarkable for two 
teeth on the one valve, placed like the letter V, the base 
toward the beak, and two impressions on the other valve. 
It occurs in the Indian Seas. The natives polish it for or- 
naments. 
To Lamark we are also indebted for having formed the 
genus CaLcroua from the anomia sandalum of Linneus. 
The largest valve is sandal-shaped, and has at the hinge two 
or three small teeth. The other valve is small, flat, semi- 
orbicular, and resembles an operculum. It is frequent in a 
fossil state in Germany. 
Mr. Sowerby, in his valuable work on British Mineral 
Conchology, has made us acquainted with several new 
genera of fossil shells, which, by the older naturalists, would 
have been inserted in the genus Anomia. The genus PEn- 
TAMERUS is an equal-sided inequivalve bivalve, with one 
valve, divided by a longitudinal internal septum into two 
parts, the other by two septa into three parts or valves. Beaks 
incurved, imperforate. He has figured three species of this 
curious genus. 
The genus Praciostoma of Sowerby, is represented by 
the Pectenites Plagiostomus of Luid, (tab. 10, f. 639,) and 
is thus defined: “ An oblique eared bivalve, hinge destitute 
of teeth or internal pit. Line of the hinge straight in one 
valve, in the other deeply cut by an angular sinus.” He 
gives figures of two species in his first volume, the gzgan- 
tea and the spinosa; and many others have been subse- 
quently detected. 
The genus Drancuora is nearly related to the preced- 
ing, but in this the shell is fixed, and the attached valve has 
an opening in place of a beak. The other valve is beaked 
and eared. 
The anomia spinosa of Linneus probably belongs to Mr. 
Sowerby’s genus Propuctus, which he thus defines: “ An 
equilateral unequal-valved bivalve, with a reflexed, more or 
less cylindrical margin; hinge transverse, linear ; beak im- 
perforate ; one valve convex, the other flat or concave ex- 
ternally.” But many new genera must be instituted, to 
-embrace all the fossil species which would have been re- 
ferred by Linnzus to the genus Anomia. 
16. Myritus. Before proceeding to notice those new 
genera which have been formed from the Linnean mytili, 
we may state, that the three parasitical species of the Sys- 
tema Nature, belong to the genus Ostrea, to which they 
associated together in this genus both fi yiatile and marine 
shells. The former now constitute a very natural genus 
termed ANopon’, formerly referred to, of which the British 
rivers furnish several species. The muscular impressions 
are three in number. 
It was easy to perceive that the mytilus hirundo of Lin- 
nus did not belong to the true mussels, it being an in- 
equivalve shell. Accordingly Lamark has constituted a new 
genus for its reception, which he terms Ayicuta. The 
mytilus margaritiferus of Linnzus is of this genus. 
Lamark, by restricting the characters of the genus myti- 
lus to include such species as have the beak terminal, has 
in this manner separated the transverse species to form the 
genus Moprota. The mytilus modiolus of Linneus is the 
type of the genus. It is common on the British shores, 
together with the modiola discors and discrepans. We are 
at a loss to account for the scruples of Lamark (Annales 
de Museuss, vol. x.) about considering this genus as_byssi- 
ferous. Had he ever examined the figure of the type of 
the genus in tab. 53 of Zoologia Danica, all his doubts 
would have been removed. 
17. Puswa. No changes haye taken place in this Lin- 
nezan genus, except that a few new species have been added. 
In the course of our review of the Linnean genera of 
bivalves, we have exposed some of those errors which the 
Swedish naturalist committed in associating discordant spe- 
cies under the same genus. Perhaps our examination of 
the univalves will make us better acquainted with the im- 
perfections of that system, and dispose us to prize those im- 
provements which subsequent naturalists have introduced. 
18. ArconauTa. This genus, which contains but few 
species, is highly prised by collectors, who call the princi- 
pal species by the name of paper nautilus. By restricting 
the characters of this genus, so as to embrace only those 
species in which the opening is interrupted by the involu- 
tion of the spire, and in which the dorsal ridge is double, 
Lamark has been able to form the genus Carmvarta. In 
this the mouth is entire, and the dorsal ridge single. It is 
represented by the argonauta vitrea of Gmelin. 
18. Nauriztus, Since the days of Linnzus, our know- 
ledge of the muléilocular testacea has been greatly enlarg- 
ed. He contented himself with arranging all the species 
with which he was acquainted under one genus, but, in con- 
sequence of modern industry, even the genera exceed the 
number of Linnzan species. Many recent species have 
been discovered by the aid cf the microscope, among the 
sand on the sea shore, and a still greater number in a fossil 
state among the calcerous strata. These newly discovered 
kinds exhibit many different characters, and have compell- 
ed conchologists to institute so many new genera for their 
reception, that the genus Nautilus of Linnzeus appears rather 
as the head of a family or order, than as a separate genus 
of univalve shells. In this department the names of Bru- 
guiére, Lamark, Montfort, Parkinson, and Sowerby, deserve 
respectful notice ; and it is from their writings that the fol- 
lowing remarks concerning the multilocular testacea have 
been extracted. The multilocular testacea may be divided 
into three sections ; the first including those which are ob- 
viously spiral ; the second, those which are produced; and 
the third, those which are of a globular or lenticular form. 
These sections are merely provisional, and are only intend- 
ed to render more obvious and intelligible our notices of 
the genera. 
1. The spiral multilocular testacea. At the head of this 
first division stands the modern genus NauTitvs, in which 
the turns of the spire are contiguous, and the last whorl in- 
closes the others. The partitions are perforated by a tube. 
We possess on our shores several species of this genus, of 
which the JV. eréspus is the most common. 
