Description of Twelve New Fossil Species. 107 



HOLOCYSTITES ROTDNDUS, 11. Sp. 



Plate IX., fig. 3, summit view, natural size. 



fig. 3a, view of the right side, natural size, 

 fig. 36, basal view, natural size. 



Body spheroidal, swelling most upon the left side, supported upon a 

 column, and covered by about six ranges of plates. There are about 

 seven or eight basal plates, and from twelve to fourteen plates in each 

 of the succeeding four ranges. The sixth range is too much involved 

 among the apertures, on the summit, to determine from our specimens 

 the number of plates. 



The ambulacral orifice is situated centrally, upon the apex of the 

 summit, posterior to the mouth. It is subelliptical in outline, and 

 surrounded by four small arm bases. We can not determine, from our 

 specimens, the number of plates that abut upon this orifice. 



The mouth is situated sub-centrally, and directly anterior to the 

 ambulacral orifice. It is sub-circular in outline. An anal aperture is 

 observable, between these two larger openings, in the plate, which 

 abuts upon the mouth, and it is situated a little nearer to the mouth 

 than to the ambulacral orifice. 



Upon tlie summit of this species, there are a number of conical de- 

 pressions, irregularly distributed, none of which penetrate the plates, 

 so far as observed, and some of them evidently do not. On the 

 specimen illustrated there are twenty-two of these conical depressions, 

 and on another specimen of the same species, there are only twelve. 

 No function can be ascribed to them. 



Some of the plates, upon the summit, are possessed of peculiar 

 elongated pores on the outer surface, but no pores have been ob- 

 served on the other plates, though they probably exist. 



This species was collected by Prof. A. G. Wetherby, to whose col- 

 lection the type belongs, near the base of the Niagara Group, in 

 Ripley county, Indiana. 



HOLOCTSTITES SUBROTUNDUS, n. Sp. 



Plate IX., fig. 2, basal view, natural size. 



fig. 2a, summit view, only part of the plates preserved. 



Body subrotund, and possessed of a column. Plates generally large. 

 The first range of plates at the point of columnar attachment too much 

 anchjdosed, in our specimens, for accurate determination. 



The next three ranges are each possessed of thirteen plates. Those 

 covering the ventricose or posterior side of the specimen very large. 

 A plate, in the fourth range, forms part of an arm support, hence the 



