4S0 PAL2E0NT0L0GY OF NEW-YORK. 



In the sandstone of New- York the species is very rare, a single cast only having 

 been seen in all the collections made. 



PLATE XCVI. 



Fig. 1 a, b. Dorsal and cardinal views of a young specimen, which has six plications on each 

 side of the mesial fold. 



Fig. 2 a, b. Dorsal and front views of a larger specimen. 



Fig. 2 c, d. Profile and cardinal views of the Fame specimen. 



Fig. 8 a, 6. Cardinal and front views of another individual, with a higher area and less ex- 

 tended binge-line. The beak in fig. 3 a, as represented, is not sufficiently elevated. 



Fig. 4 a. Ventral valve of an old specimen. 



Fig. 4 6. Dorsal valve of the same. 



Fig. 4 e, d. Profile and cardinal views of the same specimen. 



Fig. 5. Interior of the dorsal valve. 



Fig. 6 a, b. The exterior and interior of a dorsal valve of this species. 



PLATE XCVIIL 

 Fig. 8 a, h. Ventral and cardinal view of an imperfect cast of this species. 



Geological position and locality. In the Oriskany sandstone : Albany county (New- 

 York), and Cumberland ( Maryland ). 



The preceding species of Cyrtia is presented in so many varieties of 

 form, and with such a degree of variation in the number of plications, 

 that I had regarded the specimens figured as of two distinct species. A 

 farther examination, however, with a larger number of specimens before 

 me, has convinced me that these are all varieties of a single species. 



There is yet room for inquiry in regard to the degree of variation as- 

 sumed by Spirifer arredus, or whether some of the forms occurring with 

 this one are really varieties of it ; or whether they may be a distinct 

 species more nearly related to S. cyclopterus, or perhaps a variety of the 

 latter species, which, in the sandstone, attains a Idrger size than in the 

 shaly limestone below. 



The Spirifer intermedius has not been seen in specimens sufficiently 

 well-preserved, to admit of the full determination of its more minute 

 characters. 



