22 The Fauna of the Keyser ^Iember of the 



of the valve. Brachial valve most prominent at and in front of the middle ; 

 mesial fold not conspicuous, except near the front margin. Each valve 

 marked by from eighteen to twenty-two simple, angular plications, three 

 of which are usually included in the sinus of the pedicle valve. The finer 

 markings of the shell, if they were present, have been obliterated by ex- 

 foliation. The dimensions of an average adult specimen are : Length 

 9 mm. ; width 9.5 mm., and thickness 5.5 mm." Weller, 1903. 



This small shell is very abundant in the Chonetes jersoyensis zone of the 

 Keyser member. It is distinguished from Rhynchonella transversa of 

 the Helderberg by its smaller size, and by the fact that the fold and sinus 

 are not so broad except in the larger specimens.^ It is also more gibbous 

 and less transverse. Camaroto'chia litchfieldensis also resembles Rliyncho- 

 nella neglecta from the Clinton and Niagara faunas. It differs from R. 

 neglecta in having more plications with the fold and sinus narrower only 

 in the small individuals, the sinus and fold broadening in the larger forms. 

 This fonn, which has been found in the Cobleskill of New York, has been 

 identified as R. neglecta, so closely does it resemble it. 



Occurrence. — Helderberg Formation, Keyser ]\Iember. At all ex- 

 posures of the Chonetes jerseyensis zone. 



Collection. — Maryland Geological Survey. 



Camaroixechia gigaxtea n. sp. 



Plate LXIII, Figs. 15, 16 



Description. — Shell subtriangular in outline. Width greater than the 

 length. Pedicle valve convex, greatest convexity in the umbonal region, 

 anterior to this somewhat depressed convex, beak closely incurved over 

 that of the dorsal valve. Sinus shallow and undefined posteriorly, be- 

 coming deeper and with more definite limits towards the front. Dorsal 

 valve larger than the ventral valve, extremely gibbous, greatest convexity 

 two-thirds the distance from the beak to the anterior, sloping gradually to 

 the beak and abruptly to the anterior and lateral margins. No well-de- 



^ The individual figured by Schuchert in American Geologist, vol. xxi, p. 167, 

 1903, is much enlarged, although no mention is made of that fact. 



