﻿wood] new and old middle devonic crinoids 75 



descriptions of D. triadactylus and D. aplatus shows a close corre- 

 spondence between the two. The chief difference appears to be in the 

 number of upper brachial plates in the dorsal cup. />. triadactylus is 



said t<> have on one side of each ray two distichals and on the oth< r 

 one distichal bearing on each upper edge a single palmar, while D. 

 aplatus has four distichals on one side of the ray with one distichal 

 on the other side followed by four palmars on each of its upper 

 edges. The specimens in the collection of the National Museum are 

 all from the type locality of D. triadactylus, yet they agree in the 

 number of brachial plates with I), aplatus which is from -Charles- 

 town. Indiana. An incomplete specimen from the latter locality also 

 agrees with those from Alpena so far as it is preserved. The smaller 

 number of distichals ami palmars reported for D. triadactylus may 

 perhaps he accounted for by the fact that the arms are biserial above 

 the first palmars and the small wedge-shaped plates may have been 

 counted by the author of the species as arm plates. ( )n the other 

 hand the fact that these plates are incorporated into the calyx has led 

 Miller and Gurley to count them as calyx plates. 



Respiratory pores have not hitherto been reported for D. tria- 

 dactylus, but well-preserved material reveals their presence to the 

 number of thirty or more. There seem to be no constant character- 

 istics which separate this species from D. aplatus, and the latter be- 

 comes a synonym for D. triadactylus. 



Formation and locality.— -Upper Traverse limestone: Partridge 

 Point, near Alpena, Mich. Hamilton: Charlestown, End. 



Cat. Xo. 36,024 (Rominger collection), and 26.394 U. S. X. M. 

 Also in Massachusetts Institute of Technology, Xo. 651. 



DOLATOCRINUS HAMMELLI Miller and Gurley 



1895. Miller and Gurley, 111. State Museum Nat. Hist., Bull. 6, p. 52, 

 pi. 5, figs. 4, S, 6. 



The chief difference between this species and Dolatocriuus tria- 

 dactylus appears to consist in the presence of one additional arm in 

 D. hammclli. the arm formula being 1-2 ... 2-1 ... 2-1 ... 2-1 .. . 

 2-2. Fnrther study may show that they constitnte one species, hut 

 with the incomplete material at hand their identity could not be 

 determined. 



Formation and locality. — Hamilton : Xear Charlestown, Ind. 



Cat. Xo. 653 Massachusetts Institute of Technology. 



