ECHINODERMS OF SMITHSONIAN-HARTFORD EXPEDITION — CLARK 449 



The side arm plates are Avidely separated on the oral side of the 

 arms ; on the aboral side they extend inward for about one-tliird the 

 width of the arm. The arm spines are borne on a high narrow crest. 



There are 7 arm spines. The lowest arm spine is in the form of a 

 stout hook with a long, slender, strongly recurved glassy tip beneath 

 which is a long and slender supplementary point. The uppermost 

 spine is short and more or less erect. The longest spine is the third, 

 counting from the aboral surface. The second is intermediate in 

 length between the first and the third, usually more nearly resembling 

 the third. Aborally the spines rapidly decrease in length. The 

 spines are rather slender, flattened, and rather strongly echinulate. 

 They are rather short, the longest being only about one-third again 

 as long as the width of the arm. 



The single tentacle scale, situated in the angle between the under 

 and side arm plate, is short, rhombic, not much longer than broad, 

 with a finely spinous and more or less rounded tip. The first ten- 

 tacle scale is on the third tentacle pore. 



The color is light pearl gray, the arms above with narrow bands 

 of darker on about each fourth joint. The spines and the oral 

 surface are white. 



Type. — Smithsonian-Hartford station 16, Puerto Rico, western end 

 of San Juan Island in the vicinity of Fort San Geronimo; shore; 

 W. L. Schmitt, March 27, 1937 (U. S. N. M. no. E. 5592). 



Notes. — The type specimen carries several young clinging to the 

 ventral portion of the disk by means of the strongly developed hook 

 representing the lowest arm spine. The skeleton of the young con- 

 sists of a very large pentagonal central plate with a large primary 

 radial extending outward from each of the five sides. There is a 

 smgle prominent tubercle or stump in the middle of the iimer border 

 of each primary radial. From the angles of the central pentagon the 

 sides of each radial converge to the arm base. The arms, as seen 

 from above, consist of two upper arm plates and 2 pairs of side 

 arm plates, and terminate abruptly in a small bud. The hook repre- 

 senting the lowest arm spine is well developed. Above the hook 

 on the first side arm plate are two very short and very spiny rudi- 

 ments of arm spines; there is only one of these on the second side 

 arm plate. 



OPHIOTHRIX PLATYACTIS H. L. Clark 



OpMothriw lineata A. H. Clark, Univ. Iowa Studies in Nat. Hist., vol. 9, no. 

 5, p. 54, 1921 (off Pelican Island, Barbados, 4 fathoms).— H. L. Ciakk, 

 New York Acad. Sci., Scientific survey of Porto Rico and the Virgin 

 Islands, vol. 16, pt. 1, p. 62, 1933 (possibly 0. suensonii). 



Ophiothrix platyactis H. L. Claek, Proc. U. S. Nat. Mus., vol. 86, p. 417, pi. 52, 

 figs. 3, 4, 1939. 

 ZocaZ%.— Smithsonian-Hartford station 66, Barbados (1, E. 5591.) 



