CONCHIFERA. 729 
Family IV. Malleacea. Mantle open, produced posteriorly. 
Foot conical, sulcate, mostly byssiferous. Ligament internal, often 
divided and contained in several little pits. Shell lamellose, pearly 
within, often deformed, undulato-plicate. 
We transfer also to this group the genus Vulsella, as was done by 
DesuHayes, who on the other hand removed Avicula from it, which 
genus we with Lamarck leave in this family. The characters of the 
group are not yet sufficiently determined, for the animals of these 
shells are hitherto only imperfectly or not at all known. Some 
genera exist only in the fossil state. 
Inoceramus SOWERBY. Shell inequivalve, with points approxi- 
mate. Hinge straight, incrassate, furnished with a row of foveole 
for the reception of the divided ligament. (Fossil genus.) 
Many fossil species, especially from the Chalk-period, are contained in 
this genus, whilst none from the tertiary formations are known. DESHAYES, 
as also GOLDFUSS and BrRonN, now unite the genera Catillus and Myti- 
loides of Broneniarr with this. Compare the article Znocerame of DES- 
HAYES, Dict. univ. d’Hist. nat. vit. 1846, pp. 53, 54, and Bronn Leth. 
geogn. pp. 689—696 (first edition). 
Pachymya SowErsy ? 
This genus DESHAYES united formerly with Catillus, and now with Ino- 
ceramus; compare, however, BRONN loc. cit. pp. 696, 697. There is only 
one species known, also from the chalk-formation: Pachym. gigas Sow., 
Brown Leth. geogn. Tab. 31, figs. 9 a, b. 
Perna Bruc. (Species of Ostrea L.). Shell flattened, subequi- 
valve, at the anterior side gaping, an aperture emitting the byssus. 
Hinge straight, linear, edentulous, with parallel furrows receiving 
the divided ligament. 
Sp. Perna isogonwm Lam., Ostrea isogonum L., Rumpw. Amb. Rariteitk. 
Tab. 47, fig. 5, Cuv. R. Anim., éd. ill., Moll. Pl. 81, fig. 1; Ind. Ocean i 
Perna femoralis Lam. and P. canina Lam. are, according to DESHAYEs, 
only varieties of this species.—Perna ephippium L., Guirin Iconogr., 
Moll. Pl. 26, fig. 2, &e. Some fossil species also of this genus from the 
secondary and tertiary formations are known. 
Gervillia Derr. 
A fossil genus nearly allied to Perna, of which species from the oolite- 
and chalk-period are known. P 
Crenatula LAM. Shell thin, flattened, lamellose, not emarginate 
for the passage of byssus. Hinge edentulous, linear, crenate at the 
margin, with semicircular pits receiving the ligament. 
