BIVALVIA. 263 
CocHLODESMA,* Couthouy, 1839. 
SPoONHINGE. Petiver, 1764. Bontwa. Leach, MS. 1819. Gray, 1851. 
LaTERNULA. Bolten, 1798. Garaxura. Id. 1819. 
Mya (sp.) Mont. 1803. PreripLoma. ? Sehum. 1817. 
Lieuxa (sp.) Id. 1808. AMPHIDESMA (sp.) Flem. 1828. 
AuriscaLrium. MuAlf. 1811. Turacta (sp.) Lovén. 1846. 
AnatTina (sp.) Lamk. 1809. Woodw. 1854. 
Generic Character. Shell thin, transversely ovate, slightly inequivalved, inequi- 
lateral, gaping, rather compressed, right valve the more convex. Hinge with a 
spoon-shaped process in each valve, for the reception of the cartilage, with a 
minute fissure in the umbo, through which the ligament slightly projects. 
Surface smooth, or finely granulated, especially on the siphonal side; covered in the 
recent state with a fine epidermis. Adductor muscles slightly impressed, with a sinus 
in theimpression of the mantle. 
Animal with its mantle closed, except in front, for the emission of a broad com- 
pressed foot; siphons long and slender, divided in their whole extent. 
This genus closely resembles that of Zracia, in the animal as well as in the 
shell, differing in the latter, however, by having the support for the cartilage of a more 
spatulate or spoon-shaped form, which is less intimately united along the dorsal edge, 
and in the absence from the hinge of the ossiculum. 
The name Azatina was proposed as a genus by Lamarck in 1809, taking for his 
type Solen anatinus, Linn., a shell in some respects similar to those here included, by 
having a spoon-shaped process projecting inwardly, upon which was placed its internal 
ligament. It has, however, a very wide gape, and the animal has long and wnited 
siphons, clothed with a wrinkled epidermis; while the animal of Cochlodesma has 
its siphons long, slender, and divided throughout. The animals, therefore, being 
so dissimilar, they are scarcely entitled to the same name, nor could they be 
included in the above generic diagnosis. 
I have never seen a shell with this form of hinge from any Formation of an age 
anterior to that of the Coralline Crag. 
1. CocHLODESMA COMPLANATUM, S. Wood. Tab. XXVI, fig. 3, a, 4. 
Spec. Char. Testd compressa, elongato-subovatd, levi, inequilaterali, tenui; antice 
majiore, rotundatd ; postice subtruncatd ; valvd sinistrad depressd ; sinu palliari mediocre. 
Shell compressed, elongately ovate, smooth and very thin, inequilateral; anterior 
* Etym. xoyAos, shell, and despa, ligament. 
