60 



CONCHIFERA. 



laterals indistinct in the left valve ; pallial sinus 

 very wide and deep. Animal with broad, pointed 

 foot ; siphons slender, rather long, not fringed. 



T. crassa. T. tenuis. 



balaustina. fabula. 



donacina. solidula. 



pygmsea. proxima. 



incarnata. Fig. 85 ; n. s. bimaculata. 



FAMILY VII. MACTRAD^E. 



Shell more or less three-sided, equal-valved, 

 closed, or slightly gaping ; surface nearly smooth, 

 covered with a thick epidermis ; ligament internal, 

 set in a triangular pit ; hinge with two divergent 

 teeth, and usually with laterals on each side ; pal- 

 lial sinus short, rounded. Animal with united 

 siphons, and a compressed foot. 



Lutraria (Lamk.). Shell oblong, gaping at each 

 end; cartilage-plate prominent, with one or two 

 small teeth in front in each valve. Animal with 

 mantle closed, except a moderate foot-orifice. 



L. elliptica. Fig. 86 ; J n. s. 

 oblonga. 



