278 PROCEEDINGS OP THE ACADEMY OF [1879. 



* 



1859. Onychocr. exsculptus Lyon and Casseday (Typical species). Am. Journ. 



Sci., vol. 29, p. 78. Keokuk limest. Hardin Co., Ky., and Montgomery 



Co., Ind. Synom. Onychocr. (Forbesiocr.) Norwoodi Meek and Worth. 



Geol. Rep., Illinois, vol. ii. p. 245, pi. 17, fig. 3. 

 1875. Onychocrinus magnus Wortben. Geol. Rep., Illinois, vol vi. p. 520, pi. 



31, fig. 5. St. Louis limest. Monroe Co., 111. 

 1861. Onychocrinus Monroensis Meek and Worth. (Forbesiocr. Monroensis). 



Proceed. Acad. Nat. Sci Phila., p. 130. 1866, Onychocr. Monroensis, 111. 



Geol. Rep., vol. ii. p. 244, pi. 17, fig. 7. Keokuk limest. Monroe Co., 



Illinois. 

 *1846. Onychocr. polydactylus McCoy. (Taxocr. polydactylus.) Synops. Carb., 



Ireland, p. 178, pi. 24, fig. 7. Subcarbon. Ireland. 

 *1859. Onychocr, ramulosus Lyon and Cass. (Forbesiocr. ramulosus L. and C, 



not Hall), Am. Journ. Sci., vol. 28, p. 235 Keokuk limest. Montgomery 



Co., Ind. 



10. NIPTEROCRINUS Wachsmuth. 



1868. Proceed. Acad. Nat. Sci. Phila., p. 341. 

 1873. Geol. Rep. Illinois, vol. v. p. 434. 



This genus was originally referred b} r its author to the Cyotho- 

 crinidx, with which, indeed, it agrees in some of its peculiarities, 

 but a full understanding of the true nature of its structure shows 

 that it must be classified with the Ichtliyocrinidae. The number 

 of plates which constitute the proximal ring was not then, nor is 

 now, ascertained with certainty, owing to the fact that they ex- 

 tend but slightly beyond the column, and, though we are inclined 

 to think there are but three, we cannot as yet assert it positively. 

 The first radials in some points resemble those of Cyathocrinus, 

 being exceptionally large for the Ichthyocrinidae. They have above 

 a deep rounded sinus for the reception of the second radials, on each 

 side of which, the upper margin of the plate is nearly straight and 

 not incurved. The latter peculiarity, which was noticed in the 

 original description, suggests the presence of an interradial struc- 

 ture, and the continuance of the body between the so-called free 

 radials, otherwise this part would have to be more inflected for 

 the support of the dome. That an interradial structure existed 

 in the genus, is plainly seen in a specimen of N. Wachsmuthi M. 

 and W., now before us, from which we infer that the intenadials 

 extend most probably even to the succeeding order. This struc- 

 ture alone would be sufficient to place Nipterocrinus among the 

 Ichthyocrinidae, but it has also the peculiar lunulate second ra- 

 dials, the waving sutures, and strongly marked sinuosities of the 

 arm plates, and apparently no proboscis, not even a vestige of 



