Eight Neio Species of Holocystites froui the N^iayara Group. 135 



side, one iiud uiac teutlis inches; and transverse diameter about the 

 same. 



Collected by Dr. R. R. Washburn, in the middle or lower part of the 

 Niagara Group, a few miles from Waldrou, Indiana. 



HoLOOYSTiTES PLEXUS, u. sp. (Phxte YI., figs. 2, 2a.) 



[Ety.— •fZeM"s, full, large.] 



Bod}' large and sub-cyliudrical. The upper part only of our speci- 

 men is preserved, and the right side of it is somewhat injured. The 

 summit is convex and covered with large plates. One capping the 

 apex is hexagonal; bounded on two sides, hy plates reaching the am- 

 bulacral orifice, on two sides, by two large plates, supporting part of 

 the arm bases, and on the remaining tvvo sides, hy two plates con 

 stituting part of the first range below the summit. 



The ambulacral orifice is large, sub-pentagonal, and surrounded by 

 five strong arm bases. It is situated upon the left side, at the margin 

 of the summit, which is prolonged, in that direction, so as to produce 

 a concave side on the left, below the arm bases, and to give the opposite 

 or right side of the body a longitudinal convexity. The arms seem each 

 to have rested upon three plates, and if this supposition is correct, the 

 orifice is surrounded by ten pentagonal plates. Five plates fill the 

 spaces between the larger plates supporting the arm bases and the 

 first range of plates below the summit, one of which is described above 

 as capping the apex, and another forms part of the mouth. A small 

 anal aperture is visible, at the foot of the arm base, posterior to the 

 mouth, and nearl}' in a line from the posterior part of the mouth to 

 the upper part of the ambulacral orifice. The mouth is surrounded 

 b}^ five plates, and is separated from the ambulacral orifice, by a pen 

 tagonal plate, which, on one side, constitutes part of the mouth, and 

 which is supported, upon two sides, by the adjacent plates forming 

 the rear part of the arm bases, and upon the other two sides, b}' two 

 plates, each of which forms part of the ambulacral orifice as well as 

 part of the support for the arm bases. 



The first range of plates below the arm bases passes up over the 

 right side of the summit, having an inclination to the body of the fos- 

 sil of about forty-five degrees. This range consists of eight large pen- 

 tagonal plates, one of which forms the lower part of the mouth. The 

 plates, in the next three i-anges, are large, but seem to become more 

 numerous, and to vary in form and size. The injury to the right side 

 above mentioned, prevents us from accurately determining the number 

 and form of the plates in these ranges. 



The surface is slightly granulose, and all the plates are poriferous. 

 The circumference of the specimen at the lower part of the second 



