16 



aperture on each side of each pair of arms and on each side 

 of each single arm, which gives in the species twenty ovarian 

 apertures. Some of the sutures on the vault of our specimen 



arc not distinct, and for that reason the artist has not drawn 

 all the plates. 



Only two species bearing fifteen arms have been heretofore 

 described (D. canadensis and D. triadacfylus) and they have so 

 little resemblance to lids species that it would be idle to make 

 any comparison. It is. of course, unnecessary to compare it 

 with any other described species, because the arm formula 

 alone distinguishes it. 



Pound by J. P. Hammell, in the Hamilton Group, near 

 Charlestown, Indiana, and now in the collection of Wm. P. E. 

 Gurley. 



DOLATOGRINUS ( '.Kl. ATI'S, n. sp. 



Pltile III. Fie/. 13, basal views Fig. ti. side view; Fig. l~'. sum- 

 mil view, the sutures cannot be traced an I hence the 

 plates are not shown. 



Species below medium size and elegantly sculptured. Calyx 

 hemisperical, rounding from below and expanding to the free 

 arms. Sharp angular radial ridges bearing Long sharp nodes, 

 in the middle part of each plate. The surface is Eurther orna- 

 mented by a long sharp node, in the centra] pari 6f each firsl 

 interradial, and by numerous radiating lines from the central 

 pari of each plate, from two to four lines to each abutting 

 plate. Column round, Large, and having a Large, cinque foil 

 canal. 



Basal plates form a pentagon, less than one fourth wider 

 than the diameter of the column at the surface, and extend up 

 into the calyx, in the form of a hollow cone, which is tilled 

 with the end of the column. First primary radials a little 

 wider than Long, subequal in size, and the calyx will rest on 

 the points of the central nodes on these plates. Second pri- 

 mary radials very Little wider than Long, quadrangular. Third 

 primary radials not any Longer than the second, expand to the 

 superior lateral angles, pentagonal, axillary, and in three of 

 the rays support on each upper sloping side a single cecond- 



ary radial, which is axillary and supports on each upper slop- 



ing side two tertiary radials. which arrangement gives to each 

 of these rays four arms. In the other two rays the third pri- 

 mary radials support on each superior sloping side three sec- 



