266 THE LAMELLIBRANCHIA 
Genera—Kellya, Turton ; mantle with two sutures and three orifices, the 
pedal orifice being the middle and not the anterior of the three (Fig. 187) ; 
foot linguiform ; the external gill-plate with a reflected lamella; British. 
Lepton, Turton; mantle with a single suture ; the mantle edges provided 
with tentacles ; foot with a plantar ventral surface ; commensal ; British. 
Lasaea, Leach ; a single pallial suture ; the foot linguiform and elongated ; 
the external gill-plate not reflected (Fig. 206, G); British. Hrycina, 
Lamarck; fossil from the Tertiary. Pythina, Hinds. Scacchia, Philippi. 
Sportella, Deshayes. Cyamiwm, Philippi. Famity 17. Gayz_oMMIDAE, 
Gray. Mantle more or less completely reflected over the shell. Foot 
well developed, generally byssiferous. Shell thin, gaping; the adductor 
muscles much reduced. Genera—Galeomma, Turton ; shell incompletely 
covered by the mantle; a single pallial suture ; a large azygos anterior 
pallial tentacle, and a short anal siphon present. A byssal groove in the 
foot; British. Scintilla, Deshayes. Hindsiella, Stoliczka. Ephippo- 
donta, Tate ; shell internal; a single pallial suture; gills with two gill- 
plates; commensal with the shrimp 
Aaius; Australian. The three following 
genera with an internal shell probably 
Dall; two gill-plates; a pallial suture ; 
an anterior orifice leading into a caecum ; 
no adductor muscles; sexes separate ; 
from California (Fig. 239). Scioberetia, 
a single pallial suture ; foot large, elon- 
gated, with a byssal groove ; hermaphro- 
dite and commensal with a Spatangid, 
Triphylus ; from Cape Horn. Entovalva, 
Voeltzkow (Fig. 240); mantle fairly 
open, with a single suture; foot large, 
with a posterior pore; hermaphrodite 
and ineubatory ; endoparasitic in Synapta 
(=Synapticola, Malard), Madagascar and 
Atlantic. Faminy 18. KErLLYELLIDAE, 
Fischer. Mantle with a single pallial 
suture ; anal orifice with a very short 
Fic. 239. siphon ; foot elongated ; gills with two 
Chlomydoconcha oreutti, Dall. A, dor- Unequal plates. Shell ovoid ; the liga- 
sal aspect ; B, left-side view. @.0, anal ment external ; the anterior lateral 
eave Pe aoeaeane UO: hinge tooth below the cardinal tooth. 
Genera — Kellyella, Sars. Turtonia, 
Forbes and Hanley ; British. Allopagus, Stoliczka ; fossil from the Eocene. 
Lutetia, Deshayes ; fossil from the Eocene. Faminry 19. CyRENIDAE, 
Gray. Mantle with two siphons, which are more or less intimately united 
together and have papillose orifices. The sexes separate. Shell with 
external ligament; the pallial line usually with a sinus, Freshwater 
forms. Genera—Cyrena, Lamarck. Corbicula, Megerle. Batissa, Gray. 
Velorita, Gray. Galatea, Bruguiere. Fischeria, Bernardi. Faminy 20. 
belong to this family :-—Chlamydoconcha, * 
Bernard ; gills with a single gill-plate ; | 
