488 



MOLLUSCA 



PHYLUM VI 



This gi'oup contains a great many comniensal, nestling or parasitic forms ; if indepen- 

 dent usually very active, crawling like Gastropods on a sub-reptary foot, and witli the mantle 

 edges more or less reflected over the valves. 



Family 22. Leptonidae Gray. 



Shell cellulo-crystalline with a periostmcum ; valves equal, free, smooth-edged, often 

 gaping, variahly sculptured ; adductor scars peripheral, suh-equal ; pallial line simple ; 

 area ohscure or none ; ligament parivincular, opisthodetic, exter- 

 nal, often ohsolete ; resilium usually internal, suh-umhonal or 

 oblique ; hinge-plate narrow, channelled to receive the resilium ; 

 hinge variable, typically consisting of one or two radiating 

 cardinals and a pair of lateral laminae in each valve, the 

 anterior laminae often ahsent, and the posterior frequently 

 closely adjacent to the resilium, simulating cardinals. One 

 Cretaceoiis, and a niimber of Tertiary and Recent species. 



Fio. 799. 



A, Erycina pellucida Lam. 

 Calcaire Grossier ; Parnes. B, 

 Hinge of E. foucardi Desh. 

 Lower Bocene ; Herouval. 

 Greatly enlarged (after De- 

 shayes). 



Erycina (Lam.) Fischer (Fig. 799) ; Kellia Turton ; 

 Pythina Hinds ; Lasaea Leach ; Lepton Turton ; Erycinella 

 Conrad ; Spaniodon Reuss ; Fahella Conrad, etc. Tertiary 

 and Recent. 



Family 23. Galeommatidae Gray. 



Shell without a perceptihle epidermis ; valves equal, free, widely gaping ventrally, 

 smooth or variahly sculptured ; adductor scars distant, oval, reduced ; pallial line 

 simple ; ligament usually ohsolete, resilium internal, suh-umhonal or oblique, attached 

 to an excavated chondrophore in each valve ; hinge-plate hardly 

 developed ; laterals ohscure or ahsent ; one or two cardinal teeth in 

 each valve or none. Tertiary and Recent. 



Scintilla Desli. (Fig. 800) ; Galeomma Turton ; Passyia and 

 Sportella Desh. ; Hindsiella Stol. ; Ephippodonta Täte ; Solecardia 

 Conrad, etc. Tertiary and Recent. 



Family 24. Ohlamydoconchidae Dali. scintuia paHsiensis 



Desli. Upper Eocene ; 

 Shell cellulo-crystalline without an epidermis, comprising the ^f^^TieshaYes)^^' ^^^ 

 prodissoconch with narrow, long, laminar accretions, very small ; 

 valves wholly internal, not connected, contained in laterodorsal separate capsules, without 

 hinge or hinge-plate, not attached to muscles or ligament ; ligament ahsent, resilium 

 separately encapsuled hetween the ohsolete valves, functionless. Recent ; California. 



The genus Chlamydoconcha Dali is evidently the last term in a series beginn ing 

 with forms like Lepton, and continned l)y Galeomma and Eyhippodonta, but the 

 specialisation has been carried so far tliat it may well be regarded as the type of 

 a distinct family. 



Family 25. Kelliellidae Fischer. 



Shell with a periostracum ; valves equal, free, closed, smooth externally with piain 

 m,argins ; pallial line simple ; area ohscure or none ; ligament external, parivincular ; 

 resilium external or slightly sunken ; hinge plate narrow, entire, with one or tioo 

 cardinals, and a single anterior lateral placed ahove the anterior cardinal teeth. Tertiary 

 and Recent. 



