44 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



Dimensions. — Diameter of disk 5 millimeters; length of arm 20 millimeters; width of arm 

 near disk l£ millimeters. 



Description. — The single specimen of this species thus far found is described in a footnote to 

 a list of specimens reported by F. B. Meek in 1872, and redescribed and figured by C. A. White in 

 1878. Tins specimen, which has been carefully examined by the writer, presents the upper sur- 

 face of the disk and fragments of the five arms. Upon four of the fragments the upper and side 

 arm plates are shown, and upon the fifth a small portion of the under surface with the under arm 

 plates and ambulacra! openings is preserved. 



The disk is described by Meek as "depressed, nearly circular, showing on the dorsal side ten 

 ovate-subtrigonal radial plates, that are joined together over the inner ends of the arms, so as to 

 form five pairs." A close examination of the specimen shows that the disk is made up of numer- 

 ous small imbricating plates, and that the supposed division into ten mentioned by Meek may 

 be explained by the fractured condition of the poorly preserved specimen. 



The arms are small and are, as stated by Meek, perhaps three-fourths of an inch in length, 

 although none of them are preserved entire. The upper-arm plates are wider than long and 

 hexagonal in form. The outer angles are sharp and are embraced between the upper portions 

 of the side plates. The latter are slightly swollen but are not shown in their entire length. The 

 lower arms are poorly preserved but so far as exhibited are long and narrow, nearly rectangular 

 in shape, and slightly swollen in them central portions. 



Related forms. — Some doubt exists as to the generic position of this species. So many of the 

 distinctive characters are wanting that a definite determination is quite impossible, but from the 

 apparent structure of the disk, formed of numerous imbricating plates, its reference to Ophiogly- 

 pha seems probable. The only other form, 0. texana, has, so far as can be discerned, a somewhat 

 smaller and differently constructed disk, and both the upper and under arm plates are of different 

 shape. 



Locality. — The "last foot of Bridger Peak, 4 miles north of Fort Ellis, Mont." (Meek). 



Geologic horizon. — Associated with species of the genera Gryphsea, Avicula, Inoceramus, 

 Crassatella, Pholadomya, Turritella, and Gyrodes, that denote the Cretaceous age of the strata 

 (Meek). Upper Cretaceous, most probably Colorado shale. 



Collection.— U '. S. National Museum (7820). 



Class ECHINOIDEA. 



Subclass KEGULARIA ENDOBRANCHIATA. 



Order CIDAROIDEA. 



Family CIDARIDjE. 



Genus CIDARIS Leske. 



Cidaeis tehamaensis Clark, n. sp. 



Plate IX, figure 1. 



Determinative characters. — Test unknown. Spines large and club-shabed, with rows of 

 granules extending from neck to point of spine. 



Dimensions. — Spine: Length 30 millimeters; width in thickest part 12 millimeters. 



Description. — This species is represented by a well-preserved spine that is large and club- 

 shaped. The granules are large and disposed in rows extending from the neck to the point of 

 the spine. 



Locality. — Shelton's ranch, Tehama County, Cal. 



Geologic horizon. — Knoxville formation, Lower Cretaceous. 



Collection. — U. S. National Museum (31195). 



