140 AXXALS OK IHK C'ARNKf;iE MuSEUM. 



Comparison with Otiier Species. 



The earliest known species of Cyrtina in American faunas is the C. 

 pyraviidalis Hall, a rare shell from the Niagara. Owing to the very 

 limited number of specimens, little is known of its variation, but the 

 figures in Vol. II, Pal. N. Y. , show a shell which is, in some respects, 

 more primitive than C. hamiltonensis. It is smaller and there are 

 fewer plications. The cardinal area is high, as compared with the 

 width at the hinge, flat, and has a narrow delthyrium with convex 

 deltidial plates. The length is 7.8 mm., the width at the hinge, 

 which is the greatest width of the shell, is 1 1 mm., and the height of 

 the cardinal area is 7 mm. There are 10 plications. 



The next species in point of time, is C. dalmani Hall from the 

 Lower Helderberg. This is an extremely variable species, but the 

 average specimen is smaller and has fewer plications than C. hamil- 

 tonensis. The smallest specimen figured by Hall is 2.4 by 4.3 mm. 

 and has four plications. The largest is 8 X 16 and has 14 plications. 

 An average specimen is 6 X 10.5 mm. with 8 plications. This species 

 shows more advanced characters than C. pyramidalis in having the 

 mesial lobe flat, sometimes with a depressed line, and in the greater 

 number of plications. 



Cyrtina biplicata Hall from the Schoharie grit and C. crassa Hall 

 from the Corniferous, are two large shells which retain neanic charac- 

 ters. C. biplicata does not develop any plications except those which 

 bound the sinus, but has the surface covered with fine striae. C. crassa 

 has only four plications on each side of the fold. 



C. hamiltonensis, as it occurs in the Schoharie, is small, about 8X11 

 mm. and has only six plications. 



Spirifer mucronatus Conrad. (Plate YI, Rows x and 2.) 

 Hall, Pal. N. \., IV, 1867, p. 216, pi. 34, fij^s. i to 32. 



There are about 300 specimens of this species in this collection from 

 which a series can be chosen which represents the shell in all stages of 

 growth between a size of 1.06 by 1.48 mm. and 14.8 l)y 52 mm. 



Protci^itluni. — On the beak of a well preserved dorsal valve 2 mm. 

 in length was the impression of the initial shell. It was circular, 

 somewhat convex, with a curved hinge. The diameter was 11 mm. 

 Around it were two concentric growth lines marking later growth 

 stages. One indicated a shell .25 mm. long and .27 mm. wide and 

 the other a shell .27 by .32 mm. 



