752 CLASS XII. 
Note.—Genus Neera Gray, related to the Corbulw should, on account of 
the ossicle of the ligament, be removed*to the first phalanx of this family. 
Mya lL. (exclusive of several species). Shell subequivalve, 
transverse, hiant. Left valve with single cardinal tooth large, pro- 
minent within towards the right valve, and received in the fovea of 
this. Ligament inserted in tooth and cardinal fovea. Impression of 
mantle emarginate with a deep sinus posteriorly. 
Sp. Mya truncata L., Cuemn. Conchyl. Tab. 1. figs. 1, 2, DEsH. Conchyl. 
Pl. 8, figs. 1—4; Mya arenaria L., Baster Natuurk. Vitsp. 1. bl. 72—76, 
Tab. vit. figs. 1—3, Buainv. Malacol. Pl. 77, fig. 1; on the strand of the 
N. Sea at Katwijk, Scheveningen, the Swedish coasts, &c.—There are 
some fossil species of Mya in the newer tertiary formations, in which also 
the two living species mentioned are met with. 
Family XX. Pholadomyacea. Mantle sacciform, produced 
posteriorly into two elongate conjoined trachez, perforated ante- 
riorly by a narrow aperture, emitting the small foot. Shell hiant 
at both ends. Ligament external. ‘Two muscular impressions 
remote. 
Pholadomya SowrErsy, Desu. Shell thin, transverse, longer 
posteriorly, obtuse anteriorly. Hinge edentulous, inflected. Im- 
pression of mantle excised posteriorly by a deep simus. 
Sp. Pholadomya candida Sow., Dusu. Conchyl. Pl. 4, figs. 4—6; a W. 
Indian species still extremely rare in collections. The fossil species of this 
genus, that occur in almost all geological formations, are numerous, most 
so in the Lias. To these also DEsHAYES refers the genera Lysianassa MUEN- 
stpr, AGAssiz, and Platymya AGAsstz. Comp. AGASSIZ Etudes crit. sur 
les Mollusques, 2¢ livraison, Neufchatel, 1842, &c. 
Ceromya AGASS., DESH. (and Grreslyia AGASS.). 
Fossil species. 
Glycimeris Lam., Cystodaria Dauptn. Shell thick, trans- 
verse, inequilateral, shorter posteriorly, rounded at both ends. 
Hinge edentulous. Impression of mantle not excised posteriorly, 
very distinct, with margin incrassate, undate. 
Sp. Glycimeris Siliqua Lam., Mya siliqua SpENGLER, CHEMN. Conchyl. Tab. 
198, fig. 1934, Buainv. Malac. Pl. 80, fig. 3; comp. AUDOUIN Mém. sur 
PAnimal de la Glycimére, Ann. des Se. nat. Tom. 28, 1833, pp. 331—343, 
Pl. 14,18. Hitherto the only known species of this genus; on the coasts 
of Newfoundland, 
ie. 
