268 



Report of the State Geologist. 



was found. The extremely limited vertical distribution of this important 

 species is remarkable, and accords well with what has been observed else- 

 where. In the Livonia salt shaft section (13th Annual Kept. N. Y. State, 

 Geol. Vol. 1, p. 145) it is recorded from the Encrinal limestone only 



90. Stropheodonta concava, Hall. 



1867, Hall, Pal. N. Y., vol. 4, p. 96, pi. 16. 



(See also vol. 8, pt. 1.) 



This species is common in the S. demissa bed, where it attains its usual 

 large size and form. It does not commonly occur above this bed, though a 

 single specimen has been found in the Encrinal limestone on the lake-shore. 

 Several specimens were found immediately below it, and others in the shale 

 and calcareous beds between the Trilobite and Pleurodictyum beds. 



91. Stropheodonta (Leptostrophia) perplana, Conrad. 

 1867, Hall, Pal. N. Y., vol. 4, p. 98, pi. 11, 12, 17, 19. 



1892, J. Hall and J. M. Clarke, Pal. N. Y., vol. 8, pt. 1, p. 284. 



This species has a greater vertical range than either of the preceding, 

 appearing in the shale and limestone down to the Strophalosia bed. It is 

 common and occasionally abundant throughout the Lower shales, and occurs 

 in considerable numbers in the S. demissa bed, though it is by no means as 

 common as S. demissa. In the Encrinal limestone it is abundant, and it like- 

 wise characterizes the lower two or three feet of the Moscow shales. The 

 specimens in this shale are usually large and well formed. 



92. Stropheodoxta (Douvillixa) ustequtstriata, Conrad. 



1867, Hall, Pal. N. Y., vol. 4, p. 106, pi. 18. 



1892, J. Hall and J. M. Clarke, Pal. N. Y., vol. 8, pt. 1, p. 284. 



This species has a somewhat greater vertical range than the preceding. 

 It appears first in the shales and limestones above the Strophalosia bed, and 

 is not uncommon in the Trilobite beds. The rock between these and 

 the S. demissa bed has, however, furnished no specimens. In the 

 S. demissa bed it becomes abundant, appearing as gibbous specimens ranging 

 in width up to an inch or more. It is scarcely less abundant than the S. 

 demissa. Above this bed it is far less numerous, and in the Encrinal lime- 

 stone it is outnumbered by S. perplana. It appears to be absent from the 



