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 

 witliin, often deformed, undulato-plicate. 



We transfer also to this group the genus Vulsdla, as was done by 

 DESHAYES, 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 foveolse 

 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 BRONN, now unite the genera Catillus and Myti- 

 lo'ides of BRONGNIART with this. Compare the article Inocerame of DES- 

 HAYES, Diet. univ. d'ffist. nat. vii. 1846, pp. 53, 54, and BRONN Leth. 

 geogn. pp. 689 696 (first edition). 



Pachymya SOWERBY 1 



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., 

 BRONN Leth. geogn. Tab. 31, figs. 9 a, 6. 



Perna BRUG. (Species of Ostrealj.). 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 isogonum LAM., Ostrea isogonum L., HUMPH. Amb. Rariteitk. 

 Tab. 47, fig. J, Cuv. R. Anim., ed. ill., Moll. PI. 81, fig. i; Ind. Ocean; 

 Perna femoralis LAM. and P. canina LAM. are, according to DESHAYES, 

 only varieties of this species. Perna ephippium L., GU^RIN Iconcgr., 

 Moll. PL 26, fig. 2, &c. Some fossil species also of this genus from the 

 secondary and tertiary formations are known. 



Gervillia DEFR. 



A fossil genus nearly allied to Perna, of which species from the oolite- 

 and chalk-period are known. 



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. 



