THE LA MELLIBRA NCH1A 



265 



nent. Genus Callocnrdia, Adams ; abyssal. FAMILY 10. LUCINIDAE, 

 d'Orbigny. The anal orifice of the mantle sometimes produced into a 

 siphon. Anterior adductor muscle within the pallial line. Labial palps 

 very small. Gills without an external plate. Shell rather thin. Genera 

 Lucina, Bruguiere ; mantle with two sutures ; visceral mass smooth ; 

 foot vermiform ; British. Montacuta, Turton ; shell with a single suture, 

 foot short, byssiferous ; visceral mass with arborescent projections ; 

 British. Cryptodon, Turton ; mantle with a single aperture ; foot short ; 

 visceral mass smooth. FAMILY 1 1 . CORBIDAE, Call. Shell thick with 

 denticulated borders. The anal orifice provided with a valve, but not 

 with a siphon. Foot elongated 

 and pointed. Genera Corbis, 

 Cuvier. Gonodon, Schafhautl ; 

 fossil from the Trias and Juras- 

 sic. Mutiella, Stoliczka ; fossil 

 from the superior Cretaceous. 

 FAMILY 12. UNGULINIDAE, 

 Adams. Mantle without siphons ; 

 the pedal orifice long. Foot 

 greatly elongated, vermiform, 

 ending in a glandular enlarge- 

 ment (Fig. 238, III). Anterior 

 adductor muscle in contact with 

 the pallial line. Gills with two 

 plates ; labial palps small. Marine. 

 Genera Ungulina, Daudin ; FlG- o 3g- 



mantle with a single suture ; vis- Axllliaflejcuwuit , Montagu> viewed fro ,n the left 



Ceral mass smooth. DiplodontCt, side. I, anterior adductor muscle ; II, glandular 



T> .1 -.1 . portion of the mantle; III, foot; IV, gonad pro- 



Bronn ; mantle With two sutures ; jecting into the pallial cavity; V, internal plate 



British. AxinilS, Sowerbv ; mantle of the S' 11 : VII > posterior adductor muscle ; VIII, 



. . . , . , rectum; IX, posterior retractor of the foot; X, 



With a Single Suture ; Visceral mass anterior retractor of the foot. 



with arborescent excrescences (Fig. 



238); British. FAMILY 13. CYRENELLIDAE, Fischer. Mantle provided 

 with two elongated, united, non-retractile siphons. Two gill-plates to 

 each gill ; labial palps elongated. Inhabitants of fresh water. Genera 

 Cyrenella, Deshayes. Joanisiella, Dall. FAMILY 14. TANCREDIIDAE, 

 Fischer. Shell elongate, sub-triangular ; the ligament external. Hinge 

 with two cardinal teeth on the right and one or two on the left valve. 

 Posterior lateral teeth stout. An extinct family ranging from the Trias 

 to the Cretaceous. Genera Tancredia, Lycett ; Trias to Cretaceous. 

 Meckia, Gabb ; Cretaceous. FAMILY 15. UNICARDIIDAE, Fischer. Shell 

 sub-orbicular, more or less ventricose, nearly equilateral, with concentric 

 striae ; pallial line simple ; hinge with a single cardinal tooth on each 

 valve. An extinct family ranging from the Carboniferous to the Cre- 

 taceous. Genera Unicardium, d'Orbigny ; Trias to Cretaceous. Scaldia, 

 de Ryckholt ; Carboniferous. Pxeudedmondia, Fischer ; Carboniferous. 

 FAMILY 16. LEPTONIDAE, Gray. Shell thin, not covered by the mantle 

 and not gaping. Mantle without siphons ; gills with two gill-plates ; foot 

 long and byssiferous. Marine, hermaphrodite and incubatory animals. 



