34^ 



NORTH AMERICAN INDEX FOSSILS. 



CXIII. Parazyga Hall and Clarke. 



Differs from Trematospira externally only in the usually smaller 



and simple plications and in the surface covering of very fine and 



short spines ; these are usually broken off, leaving only their bases. 



Internally it has a weak deltidial tube similar to that in Hustedia. 



Cardinal process low, bi- 

 lobed ; dental sockets broad. 

 Devonic. 



395. P. hirsuta Hall. (Fig. 

 444, a— c.) Devonic. 



Depressed orbicular. 

 Pedicle valve curving regu- 

 larly to the apex where it 

 is terminated by a circular 

 foramen. Surface marked 

 with 30 to 40 low striae 

 which are most conspicuous 

 towards the margin ; these 

 are crossed by fine concen- 

 tric growth lines and more 

 distant lamellae. Shell punctate. 



Onondaga and Hamilton of New York, Kentucky, Indiana, 

 Ontario. 



CXIV. Eumetria Hall. 



Differs from Rhynchospira (No. CIX) merely in the greater com- 

 plication of the parts of the hinge plate and in the variation in the 

 form of the loop. Punctate. Mississippic to Carbonic. 

 396. E. marcyi (Shumard). (Fig. 444, d-e.) Mississippic. 



Longitudinally ovate, almost equally biconvex. Beak of pedicle 

 valve elevated and incurved and with a circular foramen. Surface 

 marked by about 50 rounded, punctate striae. 



St. Louis and Kaskaskia of Tennessee, Missouri, Arkansas, 

 Indiana, Iowa, Illinois. 



CXV. Whitfieldella Hall and Clarke. 

 Small, ovate or elongate, subequally biconvex. Beak of pedicle 

 valve not high. Cardinal slopes of both valves broad and not dis- 

 tinctly defined. Anterior margin subtruncate. Median septum 

 present in brachial valve. Surface smooth. Siluric-Devonic. 



FlG. 444. a-c, Parazyga hirsuta (Pal. N. 

 Y., II); a-e, Eumetria marcyi (Ind. Geol. 

 SurvO. 



