No. 89.] 



93 



Fig. 1 & 2 <are of the exterior, and 3, 4 the interior and cast of Athyris spirifzroides of the 

 Hamilton group, N.York. 



Fig. 5, & 7 ; Dorsal, front and profile Aiews of MeristeUa princeps of the Lower Helder- 

 berg. 8, 9 are the interior and cast of the ventral valve as shown in M. nasuta 

 (Atrypa nasuta, Conrad) of the Upper Helderbcrg limestones of New-York and 

 Ohio. The letter x refers to the filling of the rostral cavity; t, the cavities of the 

 dental lamellae; r, the triangular muscular impression. 



Xt___^- 



13 



t.^J 



_s# 



Fig. 10 & 11. Dorsal and profile views of Merista typa (Camarium typunv) : 12, interior of 

 the ventral valve; 13, longitudinal section : o, rostral cavity ; s, transverse arch- 

 ing septum, ov " shoelifter^^ proecjis of King; f, teeth. 



