Heterocrinus isodactylus. 27j9 



the body, at the expense of the upper end of the arms and pinnules. 

 Dr. C. A. Miller has a splendid specimen on a small slab which clearly 

 shows the bifurcation of the arms on the twelfth plate from the cup or 

 third radial, while this specimen shows the bifurcation on the ninth 

 plate. The specimens are about the same size and otherwise present 

 the same appearance. 



Heterocrinus isodactylus — (S. A. Miller). 



Fig. 21. Heteroennusisodaclylus. Natural size. 



Body small and tapering but very little to the column. Basal pieces 

 pentagonal, about 1^ times as wide as long; first radial pieces longer 

 than wide and quite convex longitudinally ; second radials nearly as 

 long as wide and longitudinally convex. 



The arms bear a striking resemblance to those of if. heterodactijlus, 

 but as I have only one specimen showing the arms, and it being some- 

 wdiat imperfect, I am unable to designate the particular diffei-euces if 

 any exist. It will be observed, that the basal pieces are proportional- 

 ly wider, and the first radials proportionally longer, in this species, 

 than they are in H. heterodactijlus. 



Column very large in proportion to the size of the body, round or 

 sometimes slightly pentagonal, and composed, near the head, of alter- 

 nately thicker and thinner pieces. It is from the character of the 

 column, that this species may be readily separated, from the H. Jieter- 

 odactylus, which it most resembles. The column is usually quite round 

 though sometimes it is slightly pentag(mal, the plates, however, are 

 continuous discs and show externally no separation into pieces, such 

 as always characterize the H. heterodactylus. 



■ The specimen figured is an unusually large one. Some specimens 

 have not half the diameter of this one. Its range is from low water 

 mark at Cincinnati to the top of the hills but specimens are quite rare. 



This species has been called isodactylus for the past two or three 

 years, though it was never before figured or described. I have re- 

 tained the local name though the species is not egnol fingered. 



