PLATE 3 8. 



Page. 

 Fig. 1. Tancredia Americana 142 



1, a. An outside- view of ;i large right valve, the central portion of which has been broken out 

 so as in expose tin' internal east and show the thickness of the shell. 



1,6. An outside view of the lelt valve of tbe type-specimen, with the anterior extremity 

 broken away. 



1, o. A hinge view of another very imperfect specimen of a lelt valve, considerably worn, so as 

 to blunt the teeth, and give a rather unnatural appearance to the beak and the pit 

 for the reception of the principal cardinal tooth of the other valve. 



l,rf. A dorsal view of same. [The posterior margin behind the lateral tooth is not represented 

 by the straight edge seen there, which is merely the broken edge, of the rock filling 

 the shell, the margin of which is seen above this, making a curve corresponding to 

 the left edge of the posterior hiatus.] 



1,6. An internal cast of a. large right valve, showing dimly the pallia] line, which, however, 

 is made to appear too slender. 



1,/. An outside view of an imperfect small left valve. 



I, y. A dorsal view of same, showing the hinge-teeth in profile. 



1, li. An inner view of same, showing hinge-teeth and pit, the latter not represented quite tri- 

 angular enough. 

 Fig. 2. MvTii.rs subarcuatus 69 



•J, a. A dorsal view of the internal cast of the typo-specimen. 



2.h. A left-side view of same. 



Fig. - ( bis. I Ixockkamiis Crifsii, var. subcomfres.sus 48 



An internal cast of a left valve. [Type of the variety.] 

 Fig. :'>. INOCERAMUS PKRTEXUIS 47 



'A, it. An anterior view of a specimen, with the two valves united ; portions of the shell about 

 the uuibones being worn away. 



3, It. A light -side view of I lie ty pe-spec illicit of same. 



