THE LAMELLIBRANCHIA 



267 



CYCLADIDAE, Clark. Mantle with one siphon or with two free siphons, 

 which have simple orifices. Hermaphrodite ; the embryos incubated in 

 the external gill-plate. Shell with a simple pallial line. Freshwater. 

 Genera Cyclas, Bruguiere ( = SpAam'Mw) ; two siphons ; British (Fig. 218). 

 Pisidium, Pfeiffer ; a single anal siphon ; British. FAMILY 21. RANGIIDAE. 

 Mantle with two short siphons united at their bases, and with papillose 

 orifices. Foot linguiform. Shell with prominent umbones and an 

 internal ligament. Genus Hunyia, Desmoulins ; from brackish water 

 in Florida. FAMILY 22. CARDINIIDAE, Zittel. Shell elongated, inequi- 

 lateral, the posterior side being the longer ; the ligament external ; the 

 pallial line simple ; dimyarian. An extinct family, ranging from the 



on/ 



FIG. 240. 



Entovalm, left-side view, a, anus ; c.g, cerebral ganglion ; f.gl, foot-gland ; g.gl, gonad ; i.r, 

 incubatory chamber ; in, intestine ; I, liver ; m, mouth ; pa, mantle ; sh, shell. (After 

 Voeltzkow.) 



Devonian to the Cretaceous. Genera Cardinia, Agassi/ ; Trias and 

 Jurassic. Anthracosia, King ; Carboniferous and Permian. Anoplophora t 

 Sandberger ; Trias. Pachycardia, Hauer; Trias. FAMILY 23. MEGA- 

 LODONTIDAE, Zittel. Shell inequilateral, thick, dimyarian, with pro- 

 minent umbones the posterior adductor impression borne on a myo- 

 phorous apophysis. An extinct family, ranging from the Devonian to 

 the Cretaceous. Genera Meyalodon, Sowerby ; from the Devonian to 

 the Jurassic. Pachyrisma, Morris and Lycett ; Trias and Jurassic. 

 Durya, Bohm ; Jurassic. Dicerocardium, Stoppani ; Jurassic. FAMILY 24. 

 UNIONIDAE, Fleming. Mantle with a single pallial suture and no 

 siphons. Shell equilateral, with lateral hinge teeth or no hinge 

 teeth. Inhabitants of fresh water. Development through a glochidium 



