FOSSILS OF THE N'lAGARA GROUP. 125 



proach tumidit}^, the convexity extending over the entire surface with- 

 out channeling or champering of the edges. The general surface of the 

 hody is smooth, or very finely gran'dlose. 



The above characters of the external surface and form of plates are 

 taken from gutta-percha impressions made in the natural molds left in 

 the rock by the removal of the substance of the crinoid by solution, and 

 differ very materially from the casts of the interior of the body, as 

 usually found. These casts occur not uncommon in the form of fxattened 

 or depressed spheres, or oblate bodies, preserving only the markings of 

 the suture lines, without showing any of the external features other 

 than the arrangement of the plates, while these even are mostly obscure, 

 and can only be traced with difhculty. But where the matrix can be ob- 

 tained, and impressions made in them, the true features of the siDecies 

 are obtained. At present we know nothing of the arms of the species or 

 the form of the column. 



Formation and locality: In the limestones of the Niagara group, near Greenville, 

 Darke county, and at Cedarville, Greene county, Ohio. Collected by Rev. H. 

 Hertzer. 



Genus SACCOCRIrsUS, Hall. 



(Pal. N. Y., Vol. IV., p. 205, 1852.) 



Saccocrinus Tennesseensis. 



Plate 6, fig. 10. 



Saccocrinus Tennesseensis, Troost, iMS., p. 29. 



Body elongate obconical, gradually enlarging from the base to the 

 origin of the free arms, or sometimes slightly inflated above the middle, 

 or near the arm bases. Dome flattened, constricted between the arm 

 bases, and surmounted by a small central or sub-central proboscis. 

 Plates of the body elongate, those of the radial series being much longer 

 than wide ; the second radials hexagonal, the third heptagonal in 

 most, if not all, cases. Supraradials smaller than the upper radials, two 

 in each series, arranged one above the other, the uppermost being a 

 bifurcating plate, and supporting on each sloping face a smaller plate, 

 from which rises the free arms, thus giving four arms to each ray at their 

 origin, or twenty to the entire body. Interradial series consisting of a 

 single first plate, which is intermediate in size between the first and sec- 

 ond radials, and hexagonal in form, supporting two plates in the second , 

 and subsequent ranges, to the number of five ranges, the plates in each 



