1923J Clark, Echinoderms from Lower California 155 



is, no other course seems right than to refer it to the cosmopolitan 

 squamata. There was no representative of the genus in the earlier col- 

 lection. The present specimen bears the label — "Middle of east side of 

 Cerros Island, March 12, 1911." This island is off the western coast of 

 Lower California. 



Ophiacantha normani Lyman 

 Ophiacantha normani Lyman, 1879, Bull. Mus. Comp. Zool., VI, p. 58. 

 There are 51 additional specimens of this common brittle-star from 

 Station 5694. They range from 9 to 17 mm. across the disk. 



Ophiacantha parasema 1 , new species 

 Disk about 22 mm. in diameter and 8 to 10 mm. thick; arms all broken near base, 

 4 to 5 mm. wide, the longest basal piece little more than 10 mm. long. Disk covered 

 with a rather thick soft skin, the surface of which bears numerous crowded, more or 

 less circular, minute plates, each of which carried a single, very acute, slightly rough 

 spine. These spines are relatively thick at the base and taper to the sharp point; 

 they are considerably longer than the diameter of the plate and hence the disk appears 

 to be crowded with them. The longest are about a millimeter in length. Radial 

 shields completely concealed and apparently wanting, but when the inner surface of 

 the disk is examined, they can be detected as thin, flat plates, about 3 mm. long and 

 half as wide, lying side by side, nearly parallel but scarcely in contact. 



Upper arm plates quadrilateral, overlapping, with distal margin strongly con- 

 vex and lateral margins converging proximally. The basal plate has a slightly 

 convex proximal region and the lateral margins are a little concave. It is about as 

 long as wide, but all the succeeding plates are much wider than long. There are, 

 however, only half a dozen upper arm plates on the longest arm fragment present and 

 it is hard to say how much of their shortness and overlapping is due to the highly 

 contracted condition of the arms. For the three fragments that are still attached 

 to the disk are pulled back dorsally so strongly that the upper surface rests against 

 the disk, much as occurs in the usual specimens of Ophiotholia, and, when forcibly 

 laid down horizontally, their upper surfaces are markedly concave from the evident 

 contraction of dorsal muscles. Side arm plates moderately large, the spine-bearing 

 ridges prominent, not meeting above, but apparently meeting narrowly below between 

 the under arm-plates. It is possible however that in a relaxed arm, lying horizontally, 

 the distal margin of the under arm-plates would overlie and conceal the side arm 

 plates in the median line. Each side arm plate bears 6 or 7 arm-spines, of which the 

 uppermost is probably the longest, or the next to the uppermost perhaps, and the 

 lowest shortest; as all are broken, neither their actual nor relative lengths can be 

 determined. They are glassy, acicular, longitudinally ridged and somewhat rough, 

 but not thorny; the longest was evidently longer than the arm segment and appar- 

 ently equalled two segments at least. Under arm plates small, depressed at center 

 so that they are distinctly concave, quadrilateral, with rounded corners and concave 

 lateral margins. They are not in contact in the present condition of the arms. 



Wap&arniot =8purious, in reference to its not being a typical member of the genus. 



