250 



Repoet of the State Geologist 



size. It is extremely rare below this limestone, a few crushed specimens only 

 having been found in the shale about twenty feet below the Strophalosia 

 bed. The species may be regarded as practically restricted to the Stropha- 

 losia bed, characterizing it wherever exposed. 



LAMELLIBRANCHIATA. 

 Genus Aviculopecten, McCoy. 



34- Aviculopecten pkinceps, Conrad. 



1884, Hall, Pal. X. Y., vol. 5, pt. 1, p. 1, pis. 1, 5, 6, 24, 81. 



This species occurs in the Trilobite beds, and rarely in the shale 

 immediately below. A small left valve from the Trilobite beds measured: 

 length, .">.") mm., height, .">() mm., length of hinge, 26 mm. A larger specimen 

 from these beds on the lake shore measures: length, 59 mm., height, 55 mm., 

 length of hinge, about 35 mm. In the shales above these beds fragments of 

 both valves occasionally occur. Similarly in the S. demissa bed, a number of 

 fragments, as well as perfect valves were obtained. A specimen of a right 

 valve measured 36 mm. in height, with length and hinge nearly the same. A 

 few specimens, chiefly internal moulds, were obtained from the Encrinal 

 limestone. 



35. Aviculopecten exacutus, Hall. 

 1884, Hall, Pal. N. Y., vol. 5, pt. 1, p. 8, pi. 3. 



This species is rare and represented by fragments obtained from the 

 shale down to seventeen feet below the Encrinal limestone. In the S. demissa 

 bed it is more abundant and a number of impressions and internal moulds were 

 obtained, the shell being only rarely preserved. The usual size of the 

 specimens is below the average for the species. 



Genus Pterinopecten, Hall. 



36. Pterinopecten conspectus, Hall. 



1884, Hall, Pal. N. Y., vol. 5, pt. 1, p. 66, pi. 17. 



This species is comparatively rare in these shales, the specimens obtained 

 being mainly fragments and impressions. A specimen was obtained from the 

 upper Pleurodictyum bed at Avery's creek. I have found it as low as seven- 

 teen feet below the Encrinal limestone at Eighteen-mile creek, and from the 

 shales between this point and the S. demissa bed several fragments and 

 impressions were obtained. In the latter bed it is somew hat more abundant 



