OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 423 



find this elongated form of the mouth shields in all the Albatross 

 specimens. 



OPH1OZONELLA CASTA (Keehler). 



Plate 78, figs. 5-8. 



Ophiozona casta KCEIILER ('04), p. 22, pi. 5, fig. 9; pi. 6, figs. 1, 2. MATSU- 



MOTO ('15), p. 82. 

 Ophiozonclla casta H. L. CLARK ('15), p. 340. MATSUMOTO ('17), p. 294. 



Locality. Albatross station 5428; eastern Palawan and vicinity; 

 30th of June Island bearing N. 62 W., 36.14 kilometers (19.5 miles) 

 distant (lat. 9 13' 00" N., long. 118 51' 15" E.) ; 2,021 meters (1,105 

 fathoms) ; April 3, 1909; gy. M. 



Two specimens (Cat. No. 41154, U.S.N.M.). 



No tes. These two specimens are somewhat different from each 

 other in their external appearance; in the larger, in which the di- 

 ameter of the disk is 7.5 mm., the dorsal surface is strongly convex 

 so that the disk is very thick and high, but in the second, which is 

 smaller and in which the diameter of the disk does not exceed 5 mm., 

 the dorsal surface of the disk is almost plane. But the arrangement 

 of the plates themselves shows such agreement that there can be 

 no question of separating the two specimens, and except for the 

 height of the disk they both agree well with the specimens collected 

 by the Siboga on which I based O. casta. In the latter the disk, of 

 which the diameter is 5 mm., although rather elevated does not 

 reach quite the height of that in the larger Albatross specimen, but 

 it is higher than that of the smaller. The only difference which I 

 x?an detect consists of the form of the mouth shields which are here 

 a little broader than long and simply triangular with the distal bor- 

 der very strongly convex. The mouth papillae decrease in height 

 from the outermost to the innermost, and the two innermost are 

 very low, although much elongated. In the larger specimen the 

 plates of the dorsal surface of the disk are more numerous than in 

 the Siboga type, while in the smaller the arrangement is almost the 

 same, and the dorso-central, which is pentagonal in form, is very 

 much larger than the five primary radials which are broadly in 

 contact with it (fig. 5). In the large example (fig. 7) the dorso- 

 central is circular, larger than the five radials, which are themselves 

 very large; these plates show a proximal angle, and their distal 

 border is very strongly convex; they are separated from the dorso- 

 central by a row of small plates, and only two of them just touch 

 the dorso-central by their proximal angle. In the interradial spaces 

 there are two large tandem plates, and the second, which is tri- 

 angular in shape and a little longer than broad, reaches the periph- 

 ery of the disk. In the radial spaces there is a large plate, the con- 

 vex distal border of which is close to the radial shields. The rest 



