488 



MOLLUSCA 



PHYLUM VI 



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

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



edges more or less reflected over the valves. 



o 



Family 22. Leptonidae Gray. 



Shell celhdo-crystalline with a 'periostramm ; vcdves equal, free, smooth-edged, often 

 gaping, variably sculptured ; adductor scars pieripheral, sub-equal ; pallial line simjde ; 



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

 nal, often obsolete; resilium visually internal, sub-ximhonal or 

 oblique ; hinge-plate narroto, 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 absent, and the posterior frequently 

 closely adjacent to the resilium, simulating cardinals. One 

 Cretaceous, and a number of Tertiary and Recent species. 



Erycina (Lam.) Fisclier (Fig. 799) ; Kellia Turtou ; 

 Pythina Hinds ; Lasaea Leach ; Lepton Turton ; Erycinella, 

 Conrad; Spaniodon Reuss; Fabella Conrad, etc. Tertiary 

 and Recent. 



Pin. 709. 



A, Erycinn pelluclda Lam. 

 Calcaire Grossier ; Parnes. B, 

 Hinge of E. foucanli Desli. 

 Lower Eocene ; Herouval. 

 Greatly enlarged (after De- 

 sliayes). 



Family 23. Galeommatidae Gray. 



Shell %dtliout a perceptible epidermis ; valves equal, free, widely gaping ventrally, 

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

 simple ; ligament usually obsolete, resilium internal, sub-umbonal or oblique, attached 

 to an excavated chondrophore in each valve; hinge -p)late hardly 

 developed ; laterals obscure or absent ; 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. ; Ephip>podonta Tate ; Solecardia 

 Conrad, etc. Tertiary and Recent. 



Family 24. Ohlamydoconchidae Dall. 



Fig. SOO. 



ScintiUa parisiensis 

 Desh. Upper Eocene ; 



Shell cellulo- crystalline without an epidermis, comprising the (^"te^peshayes)!""^" 

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

 valves ivholly internal, not connected, contained in latcrodorsal separate capsules, without 

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

 separately encapsuled between the obsolete valves, functionless. Recent ; California. 



The genus Ghlamydoconcha Dall is evidently the last term in a series beginning 

 with forms like Lepton, and continued liy Galeomma and Efhippodonta, but the 

 specialisation has been carried so fer that 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 plain 

 margins; pallial line simple; area obscure or none; ligament external, parivincular ; 

 resilium external or slightly sunken ; hinge plate narroio, entire, with one or tivo 

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

 and Recent. 



