OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 257 



the periphery of the disk and of the ventral surface are more elon- 

 gated in 0. plana, while in O. propmqua they are shorter and resem- 

 ble those usually borne on the rest of the dorsal surface, though be- 

 coming more closely crowded; the arm spines are more swollen in 

 0. plana in their terminal portion, where the denticulations are very 

 close together, while in O. propinqua they are more uniform in thick- 

 ness, with the denticulations more regularly distributed. But the 

 most important difference which separates these two species is found 

 in the length of the arms in relation to the diameter of the disk. 

 The arms are very short in 0. plana, while they are very long in 

 O. propinqua. I include for comparison photographs of two almost 

 complete specimens of O. propinqua and 0. plana, both from the 

 Sunda Islands, which show most clearly the differences in the length 

 of the arms (pi. 38, figs. 2, 5). 



The very different form of the hook formed by the first ventral arm 

 spine also furnishes an important character permitting of the easy 

 separation of the two species. The strong and thick hook provided 

 with three small branches found in 0. plana can not be confused 

 with the smaller hook furnished with from six to ten small slender 

 and crowded points following each other all along its concave border 

 in O. propinqua. 



Ophiothrix propinqua is rather widely spread throughout the 

 w r hole Indo-Pacific region ; the Investigator found it at depths down 

 to 31 meters (17 fathoms) and the Siboga dredged it among the 

 Sunda Islands in from 12 to 54 meters (7 to 30 fathoms). 



OPHIOTHRIX PROSTRATA, new species. 



Plate 39, figs. 1, 2. 



Locality. — Albatross station 5342; Malampaya Sound, Palawan 

 Island; Endeavor Point (S.) bearing S. 58° E., 0.93 kilometer (0.5 

 mile) distant (lat. 10° 56' 55" N., long. 119° 17' 24" E.) ; 26-46 

 meters (14-25 fathoms) ; December 23, 1908; gy. M. 



One specimen (Cat. No. 41023, U.S.N.M.). 



Description. — The diameter of the disk is 5 mm. ; all the arms are 

 broken off at a short distance from the base ; they are rather narrow 

 and apparently they do not reach any great length. 



The disk is rounded; the slightly convex dorsal surface between 

 the very large radial shields shows small imbricated plates with very 

 distinct outlines, rounded in the central region of the disk, but be- 

 coming very much longer in the radial and interradial spaces. In 

 the interradial spaces these plates form five or six rows, but in the 

 radial spaces there is only a single row of narrow rectangular plates 

 which separate the two shields of each pair throughout their whole 

 length. In general each of these plates carries a small cylindrical 

 55269— 22— Bui. 100 17 



