OPHIUKANS OF THE PHILIPPINE AND ADJACENT WATERS. 105 



Notes. — The diameter of the disk measures 4.5 mm. ; the arms are 

 about 25 mm. long. 



The individual agrees well with the description which I gave in 

 1904. For comparison with the following species, I am inserting 

 here four photographs of this specimen (pi. 22, figs. 1-4.) 



OPHIUROTHAMNUS EXCAVATUS, new species. 



Plate 22, figs. 5-8. 



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; gj. M. 



Two specimens (Cat. No. 41195, U.S.N.M.). 



Deselection. — In the larger specimen, which I have taken as the 

 type, the diameter of the disk is 5.5 mm. ; the arms are incomplete, 

 broken off at 15 mm. from the base; they must have been about 25 

 mm. long ; in the second specimen, which is much smaller, the diame- 

 ter of the disk is only 3.5 mm. 



The disk is rounded, but in both specimens the dorsal surface is 

 strongly depressed and forms a sort of rather deep cup delimited 

 by a sharp border ; the ventral surface is very convex. 



The dorsal surface is covered with plates which are rather large, 

 especially in the central region, becoming smaller and also very un- 

 equal on the rest of the disk ; they are somewhat imbricated. There 

 may be distinguished a large rounded dorsocentral plate, and beyond 

 it four smaller primary radial plates which are transversely broad- 

 ened and separated from the dorsocentral by a very narrow space. 

 The remaining plates are very much smaller. In the radial areas 

 following the primary radials there are two plates arranged tandem, 

 of which the more distal separates the proximal ends of the two 

 radial shields of each pair. In the interradial areas the plates are 

 irregularly arranged in three rows, and the border of the disk is 

 delimited by three rectangular plates, all having about the same 

 dimensions. Following these three plates there is another very large 

 plate which occupies almost all of the interradial space on the lateral 

 surface of the disk, which is almost vertical (fig. 5) ; this plate ex- 

 tends over the ventral surface between the genital slits as far as a 

 given distance from the mouth shields. The radial shields are 

 rather small, smaller than the dorsocentral, scarcely longer than 

 broad, and irregularly triangular, with a rounded proximal angle. 

 The two shields of each pair are in contact throughout almost their 

 whole length, and are separated inwardly by the plate which I have 

 noted above. Some of the plates of the central region, about 10 in 

 all, carry a short, thick, blunted spine, of which the surface is cov- 

 ered with fine asperities which elongate somewhat at the tip. Other 



