arm, the farrow runs up to tliti hasc of the arra whert? it doos 

 not cut oue-fourth of the thickuess of the plate, aud where the 

 pores upon the sides appear to differ from the other pores fluit 

 penetrate the plate only by being arranged externally in two 

 lines. The physiological functions of this furrow are unknown. 



We do not desire to be understood as laying any stress on the 

 word arms used above, for so far, no arms, in the true sense, 

 have been found in this genus. Instead of that we have had 

 ambulacra! spines, in some species, and in others no indications 

 of spines. In this species there may have been only spines in- 

 stead of arms possessing any kind of movement. All of the plates 

 are poriferous, some much more densely poriferous than others; 

 even the basal j^late is poriferous. The pores generally penetrate 

 the plates in pairs. 



This is a remarkable species, on account of the Y-shaped 

 furrow that connects the three arm or spine bases, and it is dis- 

 tinguished from all others by its peculiar form, size and the 

 plates covering the body. 



Found by J. F. Hammell in the lower part of the Niagara 

 Group, in Jefferson county, Indiana, aud now in his collection. 



HOLOCYSTITES 8PLENDENS, U. Sp. 



Flidc I, Fig. 7, left anterior riew or most rcntricose side: Fig-S, 

 right posierior view or least ventricose side; Fig. 9, summit rieir. 



This species is rather below medium size, balloon shaped or 

 somewhat pear-shaped and our specimen is most ventricose on the 

 left anterior side. It was sessile and the cicatrix for attachment 

 is plainly preserved. The whole body is pustulose and every 

 pustule is pierced by a pair of jwres. There are also a number 

 of large round cavities or hemispherical depressions irregulaily 

 distributed over the body, as shown in the illustrations, the pur- 

 pose of which is wholly unknown. It has been supposed that 

 they ai-e marks of disease, and that the fact that the whole order 

 of cystideans, soon after their great abundance in the Niagara 

 Group, became extinct, gave color to the supposition, but we have 

 no evidence that they are marks of disease. 



Commencing at the lower end, we have, first, a small, round 

 piece that attached to some foreign object, but which is papil- 

 lose aud pierced with pores just as the plates are above. It is 



