CRETACEOUS ECHINODERMATA. 43 



Dimensions. — Type specimen: Length 6.5 millimeters; width 4 to 5 millimeters; thick- 

 ness 3.5 millimeters. 



Description. — Two or three well-preserved specimens of the small surface plates of a Penta- 

 ceros have been found by the writer. They are so highly characteristic that their generic rela- 

 tions are clearly apparent. As no other Cretaceous representatives of this genus have been 

 found in American deposits they have been given a specific name. 



The plates are irregular in outline, the intermittent articulating surfaces on the perimeter 

 producing a roughly polygonal outline. The surface of the plates is uneven, the irregularly 

 flattened areas providing attachment for spines. The central portion of the plates is higher than 

 the truncated margins. 



Related forms. — No other American Cretaceous representatives of this genus are known, 

 and the plates can not readily be associated with any known European species. 



Locality. — Vincentown, N. J. 



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



Collection. — Johns Hopkins University (T 3014). 



Subclass OPHIUROIDEA. 

 Order ZYGOPHITTR^E. 

 Family OPHIOLEPIDIDiE. 



Genus OPHIOGLYPHA Lyman. 

 Ophioglypha texan a Clark. 



Plate VIII, figures 3a-c. 

 Ophioglypha texana Clark, 1893, II. S. Geol. Survey Bull. 97, p. 30, PI. IV, figs. la-c. 



Determinative characters. — Disk round; composition indistinct. Arms long, with wedge- 

 shaped under-arm plates about as wide as long; upper arm plates about twice as wide as long. 



Dimensions. — Diameter of disk 4 millimeters ; length of arm 50 millimeters ; width of arm 

 at disk 2 millimeters. 



Description. — The determination of this species is dependent on three fairly well preserved 

 forms that are grouped upon a single slab of limestone, all with the lower side exposed. The 

 surface upon which they rest is considerably weathered, and many of the details of structure 

 have consequently suffered. The general form of the disk is preserved, although its composition 

 can not be made out. Many of the arm plates have disappeared, leaving only the skeletal 

 pieces. Where preserved, the under-arm plates are wedge-shaped and about as wide as long. 

 The upper-arm plates, which are shown only as impressions upon the limestone, are nearly twice 

 as wide as long and have their lateral edges rounded. 



Locality. — Six miles north of Fort Worth, Tex., on the banks of Fossil Creek. Associated 

 with Ostrea quadriplicata Shumard, Stearnsia robbinsi White, and Leiocidaris hemigranosus 

 (Shumard). 



Geologic horizon. — Denison formation of the Washita group, Comanche series, Cretaceous. 



Collection. — U. S. National Museum (21884). 



Ophioglypha bridgerensis (Meek). 

 Plate VIII, figures 4a-b. 



Ophioderma? bridgerensis Meek, 1873, U. S. Geol. and Geog. Survey Terr. Rept. for 1872, pt. 2, p. 475. 



Ophioderma'! bridgerensis White, 1883, U. S. Geol. and Geog. Survey Terr. Rept. for 1878, pt. 1, pp. 8, 9, PI. XII, fig. 12a. 



Ophioglypha bridgerensis Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 



Ophioglypha bridgerensis Clark, 1893, U. S. Geol. Survey Bull. 97, p. 29, PL IV, figs. 2a-b. 



Determinative characters. — Disk composed of numerous small imbricating plates. Upper- 

 arm plates wider than long, the outer angles sharp and extending between the side-arm plates, 

 which are slightly smaller. Under-arm plates long and nearly rectangular in shape. 



