256 



THE LAMELLIBRANCHIA 



ligament internal (Figs. 200, 230). Malletia, Des Moulins ; the ligament 

 external. Nuculina, d'Orbigny. FAMILY 4. CTENODONTIDAE, Wohr- 

 mann. An extinct family from the Silurian ; the shell is nuculiform 

 and the hinge presents an uninterrupted arcuate row of teeth. Genera 

 Ctenodonta, Salter. Cuculella, Fischer. Cardiolaria, Meunier-Chalmas. 



The fossil group Palaeoconcha, Neumayr, is connected with the 

 Protobranchia through the Solenomyidae. It contains the following 

 families, all of which are extinct : FAMILY 1. PRAECARDIIDAE, Neumayr 

 Shell equivalve, with the hinge dentition of Area. Genus Praecardium, 

 Barrande ; from the Silurian and Devonian. FAMILY 2. ANTIPLEURIDAE, 

 Neumayr. Shell inequivalve ; the hinge with an obscure resemblance to 

 that of Area. Genus Antipleura, Barrande; from the Silurian. 

 FAMILY 3. CARDIOLIDAE, Neumayr. Shell equivalve and ventricose ; the 

 hinge without teeth. Genus Cardiola, Broderip ; from the Silurian and 

 Devonian. FAMILY 4. GRAMMYSIIDAE, Fischer. Shell thin, equivalve, 



ot we 



3LJLL/ A " * 



FIG. 231. 



Solenomya togata, Poli, left-side view (the left pallial lobe and gill cut away), a, anus ; ad', 

 ad", anterior and posterior adductor ; ao, aorta ; a.or, anal orifice of the mantle ; au, heart- 

 auricle ; o.y, cerebral ganglion ; /, foot ; f.e, foot elevator ; f.p, foot protractor ; //', //", anterior 

 and posterior foot retractor ; g, right gill ; hy.g, hypobranchial gland ; k, kidney ; TO, mouth ; 

 pa, mantle ; pe, pericardium ; p.g, pedal ganglion ; p.l, palp appendage ; pl.g, pleural ganglion ; 

 r.o, renal opening ; st, stomach ; v, heart-ventricle ; vi.c, visceral commissure ; vi.g, visceral 

 ganglion. 



oval, or elongate, the cardinal border thickened but without teeth. 

 Genera Grammysia, Verneuil ; from the Silurian and Devonian. 

 Protomya, Hall, from the Devonian. Cardiomorplia, de Koninck ; from 

 the Silurian to the Carboniferous. FAMILY 5. VLASTIDAE, Neumayr. 

 Shell thin, very inequivalve, the hinge without teeth. Genus Vlasta, 

 Barrande ; from the Silurian. FAMILY 6. SOLENOPSIDAE, Neumayr. Shell 

 equivalve, thin, greatly elongated, the umbones very far forward. 

 Genus Solenopsis, MacCoy, from the Devonian to the Trias. 



ORDER 2. Filibranchia. 



These are Lamellibranchs whose main character is the possession 

 of gills formed of parallel, ventrally directed, and reflected filaments. 

 The successive filaments are joined together by cilia disposed in 

 "ciliated discs" (Figs. 210, A; 232, i.f.j). The foot is generally 



