16 BULLETIN 115, UNITED STATES NATIONAL MUSEUM. 



Genus DOLATOCRINUS Lyon. 



The definition of the genus sufficiently appears in the antecedent 

 analysis. While it is there stated that the anal side is not differen- 

 tiated, and elsewhere that the symmetry of the dorsal cup is not 

 disturbed by anal structures, these statements must not be taken 

 too literally. While it is true that there are usually on the dorsal 

 side no extra plates analogous to those in the first or second inter- 

 brachial ranges of the posterior interradius which are commonly 

 called ''anal plates," yet there is unquestionably more or less dis- 

 turbance of the Dolatocrinus calyx by reason of the position and 

 gi'owth of the intestine, sufficient to produce in the calyx as a whole 

 a certain bilateral symmetry. The anal tube is always decidedly 

 subcentral; and while the interray toward which it inclines may in 

 most cases have no increase in number of plates, a comparison of 

 numerous specimens shows that the posterior interradius is very 

 often appreciably wider than the others, and its plates larger. Little 

 is known of the arms of Dolatocrinus, they having only been seen in 

 two or three specimens, except in the New York species described 

 by Hall as Cacahocrinus troosti, and referred to Dolatocrinus by re- 

 visore, which has branching arms, and should stand as a different 

 genus under Troost's name adopted by Hall, or some other. Aside 

 from this, all the species probably have simple, biserial arms, and 

 they must have been extremely fragile. 



Dolatocrinus is notable for the prominence of its first interbrachial, 

 which is the largest plate in the calyx, conspicuous alike for its size, 

 and in most species for its elaborate radiate sculpturing. It is usually 

 followed by one or two diminishing plates tandem, while the other 

 plates which appear in the interbrachial areas are fixed pinnulars, 

 some of which are so large as to lose the semblance of their primitive 

 function. This is the case with D. grandis, which has no interbra- 

 chials beyond the first, but the space which in other species is occu- 

 pied by a second interbrachial is taken by two large pinnulars resting 

 in part upon its angular distal face. The genus differs from others 

 having a similar incorporation of pinnules in their order of succes- 

 sion. In Comantlwcrinus , with uniserial arms, the pinnulation 

 begins on the second secundibrach, followed by one alternating on 

 the third, and beyond that on both margins of successive brachials. 

 In Scyphocrinus, also uniserial, the succession is alternately on secun- 

 dibrachs 2, 4, 5, 6, 7, etc. But in Dolatocrinus, with biserial arms, 

 the first incorporated pinnule leads from secundibrach 1, after which 

 the succession is alternately on 2 and 3, and beyond that on each 

 brachial of the biserial pairs. 



The column of Dolatocrinus has some striking peculiarities not 

 observed in crinoids outside of this group, but which it shares with 

 that of Himerocrinus. It is composed of very thin columnals, some 



