36 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



of each joint is slightly rounded. The crenulated surfaces form five broad petaloid areas dis- 

 tinctly rounded at the outer extremities and unite near the inner edge of the reentering angles 

 to form a double flat-topped ridge that reaches to the central canal, around which there is like- 

 wise a slight elevation. The crenulations are clearly visible on the outer surface of the column. 

 The column is perforated by a central canal of medium size. 



Related forms. — This species is quite unlike other species of American Pentacrinidse and is 

 distinguished from Pentacrinus tehamaensis Clark of the Pacific coast by its deeper reentering 

 angles. 



Locality. — Vincentown, N. J. 



Geologic horizon. — Vincentown sand of Rancocas group, Upper Cretaceous. 



Collections. — Academy of Natural Sciences of Philadelphia (1458) ; Johns Hopkins University. 



Family UINTACRINIDJ3. 



Genus UINTACRINUS 'Grinnell. 



Uintacrinus socialis Grinnell. 



Plate VI, figures 3a-h; Plate VII, figures la-c. 



Uintacrinus socialis Grinnell, 1876, Am. Jour. SeL, Sdser., vol. 12, pp. 81-83, PL IV, figs. l-2b. 



Uintacrinus socialis Meek, 1876, U. S. Geol. and Geog. Survey Terr. Bull., vol. 2, No. 4, pp. 375-378, figs. A-B. 



Uintacrinus socialis Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 21-24, Pis. I, II. 



Uintacrinus socialis Williston and Hill, 1894, Kansas Univ. Quart., vol. 3, No. 1, pp. 19-21 and diagram. 



Uintacrinus socialis Bather, 1896, Zool. Soc. London Proc. for 1895, pp. 974-1004, Pis. LIV-LVI, 13 figs. 



Uintacrinus socialis Logan, 1898, Kansas Univ. Geol. Survey, vol. 4, pp. 481^83, Pis. XXI, CXII. 



Uintacrinus socialis Beecher, 1900, Am. Jour. Sci., 4th ser., vol. 9, pp. 267-268, Pis. Ill, IV. 



Uintacrinus socialis Springer, 1900, Mus. Comp. Zool. Mem., vol. 25, No. 1, pp. 1-89, Pis. I- VIII. 



Uintacrinus socialis Schuchert, 1904, Smithsonian Misc. Coll., vol. 45, p. 450, PL CIII. 



Uintacrinus socialis Bassler, 1909, Smithsonian Misc. Coll., vol. 52, pp. 267, 269, Pis. XVII, XVIII. 



Determinative characters. — Calyx globose; composed of very thin, usually rather flat, 

 although sometimes decidedly convex plates, joined together by a very loose suture; faces at 

 times marked by faint, irregular, vertical grooves. Column wanting. Base or apical system 

 probably dicyclic, composed of centrale surrounded by circlet of basals (B) or circlet of infra- 

 basals (IB) and basals (B) as the case may be. Encircling the base and alternating with the 

 basals are five abutting radials (R) either heptagonal or hexagonal in form. Succeeding the 

 radials are two primary brachials (IBr) the second (IBr2) axillary and generally pentagonal in 

 form; separated by inter brachials (iBr) which may vary in number from 3 or 4 to 23. Branch- 

 ing from the axillary brachial are the secundibrachs (IIBr) or distichals, generally the first 

 eight of which are fixed, entering into the composition of the dorsal cup. Between the secundi- 

 brachs are intersecundibrachs (illB) or the interdistichals, which with the lower pinnulars 

 and the interpinnulars of all areas are fixed. The normal order of succession of pinnulars is 

 IIBr2 outer IIBr4 inner IIBr5 outer IIBr7 inner IIBrS outer, beyond which each brachial bears 

 a pinnule on alternate sides except where there is a syzygy, when only the epizygal is pinnule- 

 bearing. Ventral disk or tegmen composed of plates skin covered with small calcareous plates 

 or spicules. Mouth excentric, the ambulacra diverging from point near margin of disk. Anus 

 central, large and conical. 



Dimensions. — Width of calyx 6.25 to 75 millimeters; medium-sized specimen 40 milhmeters; 

 length of arms 100 centimeters. 



Description. — The writer of this paper gave in 1893 a more extended description of Uinta- 

 crinus socialis than his predecessors had done and was able for the first time to show the struc- 

 ture of the base, which was fairly well preserved on a single specimen. The small amount of 

 material at his disposal rendered it impossible to detect some important structural features 

 observed by later writers who had access to more abundant and better preserved specimens. 



S. W. Williston and B.H.Hill described better specimens of Uintacrinus socialis found by 

 E. E. Schlosson in Logan County, Kans. Williston pointed out that these were the first speci- 



