30 THE MESOZOIC ECHINODERMATA OF UNITED STATES. Ibullov. 



ten, as mentibued 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 ^ inch in 

 length, altliongh none of them are pi'eserved entire. The upper arm 

 plates are wider than long-, and hexagonal in form (PI. iv, Fig. 2h). 

 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 arm plates are poorly preserved, but 

 so far as exhibited are long and narrow, nearly rectangular in shape 

 and slightly swollen in their central portions. 



Belated forms. — There is some doubt as to the generic position of Ihis 

 species. So many of the distinctive characters are wanting that a defi- 

 nite determination in that i)iirticular is quite impossible, but from the 

 apparent structure of the disk, formed of numerous imbricating plates, 

 its reference to Ophioglypha seems probable. The only other form, 

 0. texana, has a somewhat smaller and differently constructed disk 

 so far as can be discerned, and both the upper and under arm plates 

 are of different shape. 



Locality and geological horizon. — This form is reported by Meek, from 

 the ''last foot of Bridger Peak, 4 miles north of Fort Elhs, Montana," 

 associated with undeterminable species of the genera GrypJuva, Avicula, 

 Inoceramus, Crassatella, Pholadomya, Turritella and Gyrodes, that de- 

 note the Cretaceous age of the strata. 



Collection. — U. S. I^ational Museum. 



Ophioglypha texana Clark. 

 Plate IV, Figs. la-c. 



Determinative characters. — Disk round ; composition indistinct. Arms 

 long, with wedge-shaped under arm plates about as wide as long; up- 

 per arm plates about twice as wide as long. 



Dimensions. — Diameter of disk, i incli; length of arm, 2 inches; 

 width of arm at disk, ^^ inch. 



Description. — The determination of this species is dependent upon 

 three fairly well preserved forms that are grouped u^^on a single 

 slab of limestone, all with the lower side exposed. The surface upon 

 which they rest is considerably weathered, so that many of the details 

 of structure have consequently suffered. The general form of the disk 

 is preserved, though its composition can not be made out. In many in- 

 stances the arm plates have disappeared, leaving only the skeletal pieces. 

 Where i)reserved, the under arm plates are wedge-shaped and about as 

 wide as long (PI. iv. Fig. Ic). The ui)per arm plates, which are shown 

 only as impressions upon the limestone, are nearly twice as wide as 

 long, and have their lateral edges rounded (PI. iv. Fig. lb). 



Belated forms. — Although this form can not with certainty be referred 

 to Ophioglypha, it possesses, however, many i^oints of similarity to 



