PLATE 28 A. 



PHge 



Fig. 1 a - k. Trematospira camuea (of the Niagara group). 212 



1 a. Dorsal view of a specimen of medium size. 



1 b. Ventral view of the same, showing a single small plication in the mesial sinus. 



lit. Ventral view of a specimen somewhat different in form . 



1 d. Profile view of the same. 



1 e. Enlargement of the heak, foramen and deltidium of the ventral valve, and the upper part 

 of the dorsal valve. 



1 /. Dorsal view of a shorter specimen, which has been cut transversely to show the internal 

 spires. 



1 g. Enlargement of plications, showing granulose surface and strong imbricating lines of 

 growth . 



1 h. Surface of plications enlarged, showing granulose surface without imbricating lines of 

 growth. 



Fig. 2 a-/. Trematospira simplex. 211 



2 a, b. Dorsal and ventral views of the specimen, natural size. 

 2 c, d. Front and profile view of the same. 



2 e,f. Dorsal and ventral views of a larger specimen, the lateral extremities of which are 

 broken off. 



Fig. 3 a - 1. Trematospira perforata. 208 



3 o. Dorsal view of a small specimen. 

 3 b, c, d. DorSal, vei:tral, and profile views. 



3 «,/. Dorsal and ventral views of an older specimen with a deep sinus. 

 3 g, h. Front views of a young and an old specimen, showing the shallow and deeper mesial 



sinus. 

 3 i. Ventral side of an imperfect specimen, showing the internal spire. 



3 fc. Enlargement showing the perforated beak and the junction of the valves. 



Fig. i a- e. Trematospira oostata. 210 



4 a, b. Dorsal and ventral valves. 



4 c, d. Profile and front views. 



4 e. Enlargement of the surface, showing the granulose punctate character, which is obscure 

 from the silicification of the shell. 



Fig. 5 a-/. Trematospira multistriata. 209 



5 a. An individual of medium size, having the beaks clo.sely incurved, and witliout indication 



of an area. 

 5 6. Dorsal view, where the minute perforation in the beak of the ventral valve is barely seen 



above the summit of the opposite one. 

 5 c, d, e. Ventral, front, and profile views of the same individual. 

 ■5/. The interior of a ventral valve, showing the remains of internal spires. 



