JUEASSIC ECHINODEKMATA. 29 



Determinative characters. — Imperfectly preserved forms of small size, with slender flexuous 

 arms, apparently covered superiorly with longitudinal rows of plates. 



Dimensions. — Diameter of disk 10 to 12 millimeters; length of arms 15 to 28 millimeters. 

 Description. — This interesting but doubtful form is thus characterized by Whitfield : 



The specimens are not in condition to afford a full description of their specific characters. They are of small size, 

 the rays being from three-fourths of an inch to 1£ inches long, measuring from the center of the body. The rays are 

 slender and flexuous, most of them being more or less curved in their direction and elevated along the middle, as shown 

 on a gutta-percha cast taken in a natural mold of a group of three individuals. The upper surface is subangular, and in 

 structure they are apparently composed of small uniform plates, placed in longitudinal rows. The center of the body 

 or disk is marked by an obscurely pentangular depression on the upper surface. None of the specimens show the under 

 side of the bod}' or rays, so that the characters of these parts are entirely unknown. 



The species appears to have been somewhat abundant, judging from the condition in which they are grouped on 

 the sandstone, and, although the specimens are obscure and too imperfect for positive determination and description, 

 it has been thought best to designate them by names, as they will undoubtedly prove a characteristic form over a cer- 

 tain region and of a limited horizon. The sandstone is marked by the layers in which they are found by ripple or wave 

 marks, having a width of about 3 inches, and indicates a near proximity to a shore line over the area where they were 

 obtained, and that the individuals are probably stranded specimens. A single very imperfect impression of a lamelli- 

 branchiate shell is seen on the same fragments of rock, but too imperfect for determination. 



Belated forms. — This doubtful species scarcely admits of comparison with other forms. 

 There is nothing from American Jurassic strata with which it can be closely associated. 



Localities. — East side of Spearfish Creek near its junction with the Redwater, Black Hills, 

 South Dakota (type); Freezeout Hills, Wyoming (Logan). 



Geologic horizon. — In red sandstones of Jurassic age 70 feet above the "Red Beds " (Whitfield 

 type) ; in a thin stratum of sandstone in the Jurassic bluish shale, No. 15 of the section (Logan), 

 Jurassic. 



Collections. — U. S. National Museum (325) ; Kansas University Museum. 



Subclass OPHIUROIDEA. 

 Order ZYGOPHIURiE. 

 Family OPHIOLEPIDID.E. 



Genus OPHIOGLYPHA Lyman. 



Ophiogltpha tjtahensis Clark, n. sp. 



Plate III, figure 5. 



Determinative characters. — Dorsal or aboral surface of disk composed of numerous small 

 imbricating plates with five pairs of "radial shields." Dorsal arm plates wider than high near 

 the disk, gradually becoming longer toward the extremity of the arms. Narrow lateral arm 

 plates shown on several of the arms. 



Dimensions. — Diameter of disk 8 millimeters; length of arm 10 millimeters (not entire); 

 width of arm near disk 1 J millimeters. 



Description. — The only specimen of this species contains two individuals on the same slab 

 together with a few fragments of arm plates. The aboral surface of the disk of one individual 

 and several of the arms are in a good state of preservation. Th? surface of the disk is covered 

 with a very large number of nearly equal sized imbricating jtlates of rounded form with the excep- 

 tion of the " radial shields," which are larger and elongate and stand in pairs at the head of the 

 arms. The arms are long, but all the outer extremities are broken, so that the full length can not 

 be determined. The dorsal arm plates are wider than high near the disk, but gradually lengthen 

 as the distance from the disk increases until they become longer than wide. The lateral arm 

 plates are preserved in places and appear as narrow plates more or less detached from the arms. 

 The spines are not clearly shown. 



Locality. — San Rafael River 10 miles below Castledale, Utah. 



Geologic horizon. — Jurassic. 



Collection.— 11. S. National Museum (22839). 



