Grabau — Faunas of the Hamilton Group. 



267 



Genus Orthothetes, Fischer de Waldheim. 



87. Orthothetes arctostriata, Hall. 



1867, Hall, Pal. N. Y., vol. 4, p. 71, pi. 9. 



1892, J. Hall and J. M. Clarke, Pal. N. Y.. vol. 8, pt. 1, p. 253. 



This species occurs throughout the greater part of the group, though it 

 is sparingly represented except at certain levels. It occurs at intervals and 

 rarely in the transition shales on the lake shore, and is not uncommon in the 

 beds above the Strophalosia bed, and up to the Trilobite beds. In the latter 

 several specimens were found, and others above this, at various intervals, to 

 the Encrinal limestone. I have not observed it in that rock, but it occurs 

 sparingly above it, several specimens having been found near the top of the 

 Moscow shales. It is abundant between one and three feet, and between 

 seven and twelve feet below the Encrinal limestone. Specimens occur with 

 the hinge approaching that of the next species, and the striae occasionally 

 approximate to those of the same form. 



88. Orthothetes perversa, Hall. 

 1867, Hall, Pal. N. Y. , vol. -1, p. 72, pi. 9. 

 1892, J. Hall and J. M. Clarke, Pal. X. Y., vol. 8, pt. 1, p. 253. 

 This species is rare at Eighteen-mile creek. I have found only a few 

 specimens which I can satisfactorily refer to this species. These came from 

 the /$'. demissa bed of Section I). The species occurs sparingly in the 

 Pleurodictyum beds of Avery's creek. 



Genus Stropheodonta, Hall. 

 89. Stropheodonta demissa, Conrad. 

 1867, Hall, Pal. X. Y., vol. 4, p. 101, pi. 17. 

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

 This species is, with few exceptions, restricted to about six inches of 

 shale in the upper foot of the Hamilton shales, the great majority of specimens 

 occurring from ten to twelve inches below the Encrinal limestone. (S. 

 demissa bed). The specimens are large and well formed, and occur abundantly 

 within this horizon. Two specimens only were found as low as eighteen 

 inches below the Encrinal limestone. A small brachial valve was found about six 

 inches below the Encrinal limestone, while in that rock only one specimen 



