LECAXOCRINIDAE 



20 1 



NIPTEROCRINUS Wachsmuth 

 Plate XV 



Nipterocrinus Wachsmuth in Meek and Worthen, Proc. Acad. Nat. Sci., Philadelphia, Dec, 1868, 

 p. 341. — Meek and Worthen, Geol. Surv., Illinois, V, 1873, p. 434. — Von Zittel, Handbuch Palaeon- 

 tologie, I, 1879, P- 352- — Wachsmuth and Springer, Revision Palaeocrinoidea, pt. 1, 1879, p. 55; 

 ibid., pt. 3, 1886, pp. 145, 188. — Miller, N. A., Geology and Palaeontology, 1889, p. 262. — Bather, 

 Treatise on Zoology (Lankester), pt. 3, 1900, p. 188. — Springer, Amer. Geologist, XXX, 1902, 

 P- 95 » Jour. Geology, XIV, 1906, p. 519. — Zittel-Eastman, Textbook Paleontology, 2d Ed., 1913, 

 p. 204. 



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Fig. 21. Nipterocrinus 



Lecanocrinidae with rays above radials separated by perisome only. 

 Crown elongate; calyx well differentiated. Infrabasals large, forming part of 

 calyx wall, apparently fused into a discoidal plate. No radianal or anal plates. 

 Interbrachial areas wide, occupied by perisome passing into the tegmen. Primi- 

 brachs three (or four). Radial facets not filling distal face of radials. Arms 

 dichotomous, divergent. Column large, long, cylindrical, not (or but slightly) 

 enlarging at the calyx ; with radicular cirri or branches at distal end. 



Genotype. Nipterocrinus wachsmuthi Meek and Worthen. 



Distribution. Lower Carboniferous, Burlington limestone; United States. 



This genus may be called the Carboniferous successor of Pycnosaccus, having a well- 

 differentiated calyx with both radianal and anal plates eliminated. The general habitus — 

 with large radials and narrow brachials, without regular interbrachials but the spaces filled 

 by perisome — is identical with that of the Silurian genus, and the superficial resemblance is 

 also very striking, especially to forms like Pycnosaccus zvelleri (PI. XIII, figs. 3-5). The 

 three or more primibrachs, which in that species are exceptional for the genus, are the rule in 

 Nipterocrinus. The first primibrach is relatively small and narrow, resting in a deeply 

 excavated sinus or radial facet, giving to the rays a very different aspect from those of the 

 Flexibilia generally ; and in this respect, especially in the imperfect condition in which speci- 

 mens are usually found, the genus much resembles Cyathocrinus. The presence of the 

 strongly sinuous sutures between the brachials is what first suggested to Wachsmuth the 

 doubt that this rare form could belong to that genus. In two other features, however, besides 

 the anal structures, there is a decided morphological difference between this genus and 

 Pycnosaccus. 



