THE LAMELLIBRANCHIA 



267 



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

 which have simple orifices. Hermaphrodite ; the embryos incuhated in 

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

 Genera Cyclas, Bruguiere ( = Sphaerium) ; 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. Genusp Rangia, 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 



Fio. 240. 



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

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

 Voeltzkow.) 



Devonian to the Cretaceous. Genera Cardinia, Agassiz ; Trias and 

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

 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 Megalodon, Sowerby ; from the Devonian to 

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

 Durga, 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 



