CLASS I PELECYPODA 



Palaeosolen Hall. Devonian. Leptosolen Conrad. Cretaceous. 



497 



Fi... 822. 



Solcn suhfraglKs Eichw. Miocene (Sarma- 

 tian Stage) ; Pullendorf, Hungary. 



Fic. S-23. 



CuUellus grignonensis Desh. Calcairo 

 Grossier ; Grignon, near Paris. 



Superfamily 15. MACTRACEA Gray. 



Resiliuvi internal, seated on chondrophores, left cardinal tooth bifid, fitting below the 

 two right cardinals, lohich are more or less joined together dorsally. Inner wall of the 

 mantle behind the siphons exhibiting a laminar sense organ. 



Family 38. Mactridae Gray. 



Shell 'porccllanous, xvith an obvious epidermis, usually rounded-triangular, with 

 smooth or concentrically sculptured surface, smooth margins, ctnd prominent frosogyrous 

 beaks ; valves equal, free, usually with a slight posterior gape ; area not limited ; liga- 

 ment variably external or internal; resilium connecting sub-triangulnr chondrophores 

 usucdly excavated out of the hinge-plate, rarely with a pro}) or buttress ; hinge-plate locll 

 developed, with typically an anterior and posterior lateral in the left, received into soclcets 

 or paired laminae in the right valve, or obsolete ; cardincds in the right valve two, with 

 their dorsal edges usually soldered together, and one bifid or deltoid cardinal in the 

 left, fitting below the former, a delicate accessory lamella often present in either valve, or 

 all may be more or less obsolete ; siphons toell developed, united, and usually with an 

 epidermal tunic ; adductors peripheral, sub-equal. Cretaceous to Eecent. 



This groui) is so large and its extremes so variable, that 

 it is best divided into subfamilies, as follows : ^ Mactrinae, 

 Pteropsidinae, Lutrariinac, Zcnatiinac and ? AnatincUinae. 



Mactra Linn. (Fig. 824). Ligament and resilium 

 separated by a slielly se])tum. Tertiary and Recent. 



Subgenera : Mactra s.s., Coelomactra, Mactroderma, 

 Mactrotoma Dall ; Mactrella Gray. 



Fio. 8-'4. 



Mactra podolica Eicliw. Miocene 

 (Sarmatian Stage) ; Wiesen, near 

 Vienna. 



Fio. 825. 

 Lutraria dliptica Roissy. Pliocene ; Rhode.s. ^/•j. 



Spisula Gray. Ligament and resilium not separated, the former more or less 

 external. Cretaceous to Recent. 



^ Dalt, W. IT., Synopsis of a Review of the Genera of Recent and Teitiary Mactridae and 

 Mesodesmatidae. Proc. Mai. Soc, 1895, vol. i. 



VOL. I 2 K 



