CLASS I PELECYPODA 



Palaeosolen Hall. Devoiiian. Leptosolen Conrad, Cretaceous. 



497 



Solen suhfragilis Eichw. Miocene (Sarma- 

 tian Stage) ; Pullendorf, Hungary. 



Fio. 823. 



Cultdlus gngnonensis Desh. Calcaire 

 Grossier ; Grignon, near Paris. 



Superfamily 15. MACTRACEA Gray. 



Resilium internal, seated on chondrophores, left cardinal tooth hifid, fitting below the 

 hüo right cardinals, which are more or less joined together dorsally. Inner ivall of the 

 mantle hehind the siphons exhibiting a laminar sense organ. 



Family 38. Mactridae Gray. 



Shell porcellanous, loith an ohvious epidermis, usually rounded-triangular, with 

 smooth or concentrically sculptured surface, smooth margins, and prominent prosogyrous 

 heahs ; valves eqtial, 'free, usually with a slight posterior gape ; area not limited; liga- 

 ment variahly external or internal; resilium connecting sub-triangular chondrophores 

 usually excavated out of the hinge-plate, rarely with a prop or buttress ; hinge-plate well 

 developed, with tijpically an anterior and posterior lateral in the left, received into sochets 

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

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

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

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

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



This group is so large and its extre;nes so variable, that 

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

 Pteropsidinae, Lutrariinae, Zenatiinae and ? Anatinellinae. 



Mactra Linn. (Fig. 824). 

 separated by a shelly septum. 



Ligament and resilium 

 Tertiary and Recent 



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

 Mactrotoma Dali ; Mactrella Gray. 



Fk;. S24. 



Mactra podolica Eichw. Miocene 

 (Sarmatian Stage) ; Wiesen, near 

 Vienna. 



Fi(i. 825. 

 lAUraria elliptica Roissy. Pliocene ; Rhodes. 2/3 



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

 external. Cretaceous to Recent. 



^ Dcdl, W. ff., Synopsis of a Review of the Genera of Recent and Teitiary Mactridae and 

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



VOL. I 2 K 



