420 



MOLLUSCA 



SUB-KINGDOM VI 



Superfamily 15. MACTEACEA. Gray. 



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

 two right cardinals, ^vhich 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 porcellanous, with an obvious epidermis, usually rounded-triangular, with 

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

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

 ment variably 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 normally an anterior and posterior lateral in the left, received into sockets 

 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 ilie 

 left, fitting below 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 Kecent. 



This group is so large and its extremes so variable, that it is best divided into sub-families, 

 as follows : l Mactrinae, Ptcropsidinae, Lutrariinae, Zcnatiinae, and ? Anatinellinae. 



Mactra, Linn. (Fig. 775). 

 separated by a shelly septum. 



Ligament and resilium 

 Tertiary and Recent. 



Sub - genera : Mactra s.s., Coeloinactra, Mactrodcrma, 

 Mactrotoma, Ball ; Mactrella, Gray. 



Spisula, Gray. Ligament and resilium not separated, 

 the former more or less external. Cretaceous to Recent. 



Mactra Podolica, Eichw. Miocene 

 (Sarmatian Stage) ; Wiesen, near 

 Vienna. 



FIG. 776. 

 Lutraria elliptica, Roissy. Pliocene ; Rhodes, 



Sub-genera : Hemimactra, Swains. ; Leptospisula, Call ; Cymbophora, Gabb ; tichizodcsma, 

 Gray. 



Mulinia, Gray. Ligament and resilium immersed in the same socket. Miocene 

 and Recent. 



Rangia, Desm. (Gnathodon, Gray, non Goldfuss). Like Mulinia, but with 

 elongated laterals, and the anterior lateral hooked at the umbonal end. Estuarine. 



Pteropsis, Conrad. Eocene. Labiosa (Schmidt), Moller. Miocene and Recent. 



Lutraria, Lam. (Fig. 776). Soleniform, hinge Mactroid. Tertiary and Recent. 



Tresus, Gray (Schizothaerus, Com-.) ; Eastonia, Gray ; Heterocardia, Desh. Tertiary 

 and Recent. Zenatia, Gray ; Anatinella, Sow. Recent. 



1 Cf. Dall, W. II., Synopsis of a Review of the Genera of Recent and Tertiary Mactridae and 

 Mesodesmatidae (Proc. Mai. Soc. vol. I. pp. 203-213), March 1895. 



