CONTKIBUTIONS TO PAL^ONTOLOaY. 



153 



The greater proportion of the species of Crinoidea described in the 

 preceding pages are of the collections of Mr. C. A. White, made 

 during the summer and autumn of 1860 : some are from the col- 

 lections of 1859, by Mr. C. A. White and Mr. R. P. Whitfield, made 

 for the Palaeontology of New- York. The Cacabocrinus speciosus^ and 

 some specimens of ANCYRocRiNuSjare from the State Collection; and 

 a few others, not particularly indicated, have been in my own 

 cabinet many years. 



Heretofore the species of Crinoidea known in the Upper Helder- 

 berg and Hamilton groups have been so few, that they afforded but 

 unsatisfactory evidence of the character of this fauna during those 

 geological periods. 



Several other species still remain undescribed; and from the ex- 

 perience of the past three years, I have no doubt but the Hamilton 

 group will ultimately yield a much larger number than we yet 

 know. 



The genera now known amount to seventeen, including two or 

 three which may be considered subgenera. 



The accompan3ing diagrams of Mucleocrinus elegans illustrate 

 the structure of that species, as well as of the genus. 



FiG.l. 



Fia.2. 



Fia. 1. Nat. size. The central part consists of the three small basal plates, and the five short 

 radial plates, a, The interradial plate, with the small summit plate near the apex. 6, 

 The anal plate, margined by the two narrow curving interradial plates of the anal side. 

 The linear pieces represent the pseudambulacral fields. 



FiO. 2. Summit enlarged, showing the form and relative position of the summit plates, a. 

 Anal plate ; b, indicates the smooth space, which occupies the middle of the plate, c, Tho 

 interradial plates, d, their smooth spaces, e. The irregular, curving interradial plates of 

 the anal area. 



[Senate, No. 116.] 



20 



