BIVALVIA. 269 
adductors are rather small and deep, and the mantle-mark has an irregular sinus, by 
no means large. The shell is beautifully nacreous within, and the exterior is 
ornamented with papille or granulations, studded somewhat like the barrel of a 
musical box. 
In the living state this species has been met with in deep water, while some of its 
associates in the Coralline Crag are very shallow-water forms. Mr. Jeffreys has 
dredged it off the Isle of Skye in 50, and Professor E. Forbes obtained it in the Aigean 
at the depth of 150 fathoms. 
At page 148 (ante), I had supposed the genus Z/etis to have been nearly related 
to Lucinopsis, but this allocation is probably incorrect. In Mr. Woodward’s ‘ Rudi- 
mentary Treatise of Recent and Fossil Shells,’ it is arranged in his family J/yacide. 
I think, however, the present species, Poromya granulata, cannot be correctly placed, 
as it is there, between the genera Mya and Panopea. 
Corbula gigantea, J. Sowerby, Thetis gigantea, Woodward, has a granulated exterior, 
with an external ligament, and faint or obsolete cost; and if it be not a true Pho/a- 
domya, it forms a connecting link between that genus and Thetis. 
- Panpora,* Brug. 1792. 
Hyprocma and HypoGEopErMA (sp.) Poli. Catoropium. Bolten, 1798. 
TELLINA (sp.) Linn. Trurina. Brown, 1827. 
Soxen (sp.) Mont. | 
Generic Character. Shell transverse, inequivalve, inequilateral, ovate or subrhom- 
boidal, externally smooth and of a nacreous texture, gaping at the anterior extremity, 
one valve flat, the other more or less convex. Hinge with a prominent obtuse tooth 
upon the right or flatter valve, and a corresponding depression for its reception in the 
opposite‘one. Impressions of the adductor muscles subcircular, with a small or scarcely 
perceptible sinus in that by the mantle. Ligament internal. 
The mantle is described as nearly closed, with a small passage for a narrow tongue- 
shaped foot; and the siphons are represented as very short, united nearly to their 
orifices, which are fringed, and diverging. 
The inequality of the valves and internal ligament have been considered as charac- 
ters sufficient to approximate this genus to that of Coréu/a, from which, however, it is 
sufficiently removed, as essential differences exist in the animal inhabitant, but more 
especially in the composition of its shell. In the examination and report by Dr. 
* Etym. Pandora, a proper name. This was given also to the inequivalved Pectens, probably from 
their box-like character. 
