THE LAMELLIBRANCHIA 265 
nent. Genus—Callocurdia, Adams; abyssal, Faminy 10. Lucrytipan, 
VOrbigny. 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 
—Luceina, Bruguicre ; 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. Oryptodon, Turton ; mantle with a single aperture ; foot short ; 
visceral mass smooth. Famrty 1]. Corprpas, Dall. 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.  Muttella, Stoliczka ; fossil 
from the superior Cretaceous. 
FamMILy 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 ; Fic. 238. 
mantle with a single suture ; vis- Axinus flecwosus, Montagu, viewed from the left 
eceral mass smooth. Diplodonta, side. I, anterior adductor muscle ; II, glandular 
; portion of the mantle ; III, foot; IV, gonad pro- 
Bronn 3 mantle with two sutures ; Jecting into the pallial cavity ; V, internal plate 
British, Azinus, Sowerby; mantle ofthe ttl VIL posterior adnctod muscle V1 
with a single suture ; visceral mass anterior retractor of the foot. 
with arborescent excrescences (Fig. 
238); British, Famity 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. Famity 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. 
Meekia, Gabb ; Cretaceous. Faminty 15. UNtIcarpDIIDAR, 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. Psewdedmondia, Fischer ; Carboniferous. 
Famity 16. Lepronipan, 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. 
