EOHINODERMS OF SMITHSONIAN-HARTFORD EXPEDITION — CLARK 443 



adambulacral plates united by syzygy ; proximal adambulacrals with 

 a diagonal row of 4 or 5 spines; marginals greatly reduced, widely 

 separated. 



DescHption. — The disk is 11 mm in diameter, with the borders 

 between the broad arm bases straight and only about one-quarter 

 as long as the width of the arm bases. The surface is flat and on 

 the same level as that of the abactinal surface of the rays, which is 

 continuous with it. 



The disk is completely covered with a pavement of small subequal 

 contiguous polygonal plates, each of which bears a single (more rarely 

 two) long, slender, sharj), roughened or subechinulate spinule. 

 Thickly strewn over the surface of the disk, with a tendency to 

 congregate about the spinules, are numerous very small pedicellariae 

 the tips of which are much broadened, rounded-triangular, with a 

 smooth and straight or slightly concave distal border. Wlien the 

 pedicellariae are open the long processes at the base of each blade 

 extending laterally give them the appearance of having 4 blades, 2 

 spatulate and 2, at right angles to these, pointed. 



In each of the interbrachial angles is a large, circular, swollen 

 interradial that extends from the abactinal surface halfway to the 

 actinal and occupies the entire interval between the arm bases. 

 Beneath this are two large contiguous plates representing abactinal 

 extensions of the mouth plates, which, like the interradial, span the 

 interval between the arm bases. Inunediately below the interradial 

 is a small plate lying between the abactinal ends of the two mouth 

 plates and with difficulty distinguishable from them. 



The madreporite is rather large, 1.3 mm in diameter, situated at 

 about its own diameter from the adjacent interradial plate, strongly 

 convex, and bare of spines. The opening is a rather broad oval slit 

 crossed by a few delicate calcareous bridges situated on one side. 



The anus is rather large and conspicuous, excentric, 4.7 mm from 

 the edge of the disk. 



The 6 arms are 110+ mm long, stout at the base, with a rather 

 slight fusiform swelling over the genital region, becoming slender 

 distally. They are 3.8 mm wide at the base, 5.5 mm wide in the 

 broadest part, about 11 mm from the disk; and the genital region, 

 beyond which there are no abactinal plates, is 24 mm long, or a 

 little more than twice the diameter of the disk. The arms are broad 

 actinally, narrow abactinally, with sharply sloping sides. 



The genital region is completely enclosed by a continuous pave- 

 ment of rather large rhombic, pentagonal, or hexagonal contiguous 

 plates, which are usually slightly broader than long. These plates 

 show no indication of arrangement in transverse bands, and each 

 bears in its central portion 1 to 4 or 5 (usually 2 to 4) well-separated 

 spinules resembling those on the disk. On a few of the plates at the 



