Grabau — Faunas of the Hamilton Grout. 



263 



ante-posterior diameter of the shell is 6 mm. ; the transverse diameter, 5 mm. ; 

 distance from beak to posterior margin, 2.2 mm. Several specimens of Orbicu- 

 loidea have been found in the Nautilus bed. These show radiating folds on 

 all parts of the shell, and probably represent a variety of this species. 



Genus Schizobolus, Ulrich, 



77. Schizobolus tkuncatus, Hall. 

 1867, Hall, Pal. N. Y., vol. 4, p. 23, pi. 1, 2. 



1892, J. Hall, and J. M. Clarke, Pal. N. Y., vol. 8, pt. 1, p. 87, pi 3. 



This species has, so far as I am aware, heretofore been reported only from 

 the Genesee and overlying beds. It occurs here, however, quite abundantly 

 in the upper part of the Moscow shale, where its downward limit is usually 

 marked by a layer of calcareous concretions. The lowest position in which 

 it has been found is in the middle Moscow (Orbietrfnidea media bed) of Sect- 

 ion E, where a few specimens occur with 0. media. It occurs again in this 

 shale, three feet below the Styliola limestone. The specimens found here 

 are slightly larger than the usual size. The average of six measurements of 

 specimens of the ordinary form are : length, 6.2 mm. ; width, 5.7 mm. When- 

 ever the specimens occur in the limestone layer, as at Section II, they are 

 more or less exfoliated. Nevertheless a number of specimens show the median 

 septum in the interior of the brachial valve, while the central muscular 

 scars were likewise observed in a number of specimens. These features are 

 less perfectly shown in the specimens from the shale. The majority of the 

 specimens found are brachial valves. 



Genus Craniella, CEhlert. 



78. Craniella IIamiltoni.e, Hall. 

 1867, Hall, Pal. N, Y., vol. -i, p. 27, pi. 3. 



1892, J. Hall and J. M. Clarke, Pal. N. Y., vol. 8, pt. 1, p. 153. 



This species is rather rare in the shales of Eighteen-mile creek, the few 

 specimens found being usually in a poorly preserved condition. It occurs 

 mainly in the upper part of the Hamilton shales, but several specimens were 

 found in the shale two feet below the base of the Trilobite beds at Avery's 

 creek. 



