298 Field Columbian Museum — Geology, Vol. II. 



by the beveled edges of the plates. No radial ridges are observed. 

 The natural cast is turbinate, pointed below and truncated above, 

 with prominent arm bases. Arms, judging from the arm bases, two to 

 each ray. 



Basals three, equal in size, forming a shallow cup with an hexag- 

 onal outline. Radials five, height and width about equal, the two 

 anterior laterals heptagonal, the others hexagonal, in- contact except 

 at the posterior side where they are separated by the first anal plate. 

 First costals quadrangular, height and width about equal, much 

 smaller than the radials. Second costals about the size of the first, 

 wider than high, pentangular, axillary, supporting the distichals upon 

 their sloping edges. Distichals comparatively large, two or more to 

 each ray. The first interbrachial plate is intermediate in size 

 between the radials and the first costals ; it is nine-sided and occupies 

 the space from the sloping superior edges of the radials to the inferior 

 edges of the distichals ; it supports a narrow plate upon its upper edge. 

 No interdistichals are observed. The anal interradius is considerably 

 wider than the interbrachial areas. The first anal plate is heptagonal, 

 resting on the basals between the posterior lateral radials. It is 

 followed by three plates in the second row and by five in the two 

 succeeding rows. 



In the arrangement and relative size of the plates this species 

 closely resembles H. (Pionocrinus) farctus Angelin * (See Fig. 10), but 

 that is a very small species and the plates are moderately convex and 

 without sculpturing. The distinguishing characters between this 

 species and H. farringtoni are discussed under that species. 



The type specimen ( Mus. No. P 9628 ) consists of a somewhat 

 weathered natural cast with a portion of the accompanying natural 

 mold. The mold comprises the basal cup in good condition, three 

 radials and the first anal plate practically complete and the lower half 

 of the other two radials ; in two of the rays the costals and one of the 

 distichals are preserved with the enclosed interbrachial area. The 

 impression from this mold gives the general form of the exterior 

 of the dorsal cup and the ornamentation of the plates. The form 

 of more than half of the plates can be traced on the natural cast, so 

 that the characters of the species can be ascertained. The pits on the 

 basal and radial plates, shown in PI. LXXXVII, Figs. 8 and 9, are 

 caused by protuberances in the natural mold. These protuberances 

 appear to be carbonate of lime deposited after the original crinoid 

 had been dissolved out, and probably have.no connection with the 

 ornamentation of the plates. 



* Iconographia Crinoideorum, p. 5, PI. XVI, Fig. 23. 



