OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 131 



more or less deeply over the disk, and form grooves similar to those 

 which we typically find in the genus Ophioplinthaca. However, these 

 interradial incisions or notches are not bounded by plates noticeably 

 larger than the others, and the radial shields are likewise very small. 

 It is for this reason that in 1904 I placed this species in the genus 

 Ophiomitrella. 



The Siboga discovered 0. placida among the Sunda islands at 

 depths between 204 and 304 meters (112 to 166 fathoms) ; in the type 

 of the species the diameter of the disk measured 10 mm. 



OPHIOPLINTHACA CHELYS (Wyville Thomson). 



Plate 19, figs. 3, 4. 



Ophiacantha chelys WYVILLE THOMSON ('77), p. 64, figs. 16, 17. 

 Ophiomitra chelys LYMAN ('77), p. 152, pi. 9, figs. 239-241; ('82), p. 205. 

 Ophioplinthaca chelys KGEHLEB ('04), p. 131; ('07), p. 294; ('07a), p. 324; 

 ('09), pi. 193. II. L. CLARK ('15), p. 211. 



Locality. Albatross station 5637; Bouro Island (south) and 

 vicinity; Amblau Island (N.) bearing N. 80 E., 38.92 kilometers 

 (21 miles) distant (lat. 3 53' 20" S., long., 126 48' 00" E.) ; 1,280 

 meters (TOO fathoms) ; December 10, 1909; gy. M. 



One specimen (Cat. No. 41060, U.S.N.M.). 



Notes. The diameter of the disk is 5.5 mm. ; only three arms re- 

 main attached to the disk, a single one being complete; it reaches 

 about 25 mm. in length. 



The plates of the dorsal surface of the disk bear a few large club 

 spines which are rather thick and which broaden toward their ex- 

 tremity into a disk bearing fine spinules. In his description Lyman 

 says that the plates of the disk bear " short, blunt, usually smooth, 

 stumps or spines " ; but the figure which he published in 1877 (pi. 

 9, fig. 240), in which these club spines are represented in face view, 

 show that they have a broadened extremity furnished with spinules 

 quite comparable to those which I observe in my specimen; these 

 club spines are not numerous. 



I have already described the variations which may be observed in 

 the form and in the number of the club spines of the dorsal surface of 

 the disk in the specimens of 0. chelys collected by the Siboga in the 

 Sunda Archipelago (Koehler '04, p. 131) ; certain of these specimens 

 only showed small, short, cylindrical and smooth club spines, while 

 others bore large granules with the extremity broadened, identical 

 with those which I find on the Albatross specimen. 5 



The drawings of Wyville Thomson and of Lyman are somewhat 

 schematic ; I have thought it advisable to reproduce here two photo- 

 graphs of the specimens collected by the Albatross (pi. 19, figs. 3, 4). 



6 I must correct a typographical error which I notice in the last line of page 131 of 

 my memoir of 1904. In place of " Station 135 " read " Station 227." 



