OPHIURANS OF THE PHILIPPINE AND ADJACENT WATERS. 29 



mal border; it very soon loses those on the distal border, simulta- 

 neously becoming recurved and transforming very rapidly into a 

 hook with three or four branches. These spines consist of a short 

 opaque white basal portion followed by a very much longer per- 

 fectly transparent, though brownish yellow, section. In figure 4 of 

 plate 92 is shown a number of photographs of spines from different 

 heights on the arms. 



Each tentacle pore is provided with a very small scale which is 

 easily confused with the base of the first ventral spine. 



The disk is dark brown on both surfaces, but the radial shields are 

 white. The arms are lighter ; they are brownish on the dorsal surface 

 and on the sides, and almost pure white on the ventral surface ; the 

 spines are light brown. 



Affinities and distinctive features. — Ophiobyrsella intorta can not 

 be confused with any of the species of the genus Ophiobyrsella known 

 from the Indian Ocean. Ophiobyrsella erinaceus Kcehler, found by 

 the Siboga in the Sunda Islands, is a small species in which the in- 

 tegument of the disk is entirely naked and the radial shields alone 

 are armed with spines ; the mouth papillae are rather large and the 

 arm spines, which are four in number, are elongated. The two Jap- 

 anese species which have recently been described by H. L. Clark are 

 very different. Ophiobyrsella acanthinobrachia has six or seven arm 

 spines; O. synoptacantha has on the dorsal surface of the disk numer- 

 ous little plates of which some bear a small spine ; the arm spines are 

 four in number, but the mouth shields are longer than broad and the 

 adoral plates are widely separated in the median interradial line. 



Ophiobyrsella intorta is equally distinct from all the species known 

 from the Atlantic. It recalls O. quadrispinosa Kcehler, by its well 

 developed mouth papillae, but is distinguished from it by the num- 

 ber of arm spines. Ophiobyrsella hystricis Lyman, from the Shet- 

 land Islands, has the dorsal surface of the disk armed with more 

 highly developed spines over the radial shields; the arm spines, 

 which are five in number, are rather strong and elongated, as long 

 as the arm segments, and the tooth papillae are arranged differ- 

 ently from those in the Philippine species. O. hystricis is, moreover, 

 the type of Verrill's genus Ophiobyrsa, with the mouth papillae and 

 the tooth papillae rudimentary. In O. perrieri Lyman the dorsal 

 surface of the disk is naked, the radial shields are provided with 

 small, short, and conical spines, and the arm spines are six in num- 

 ber. 



In his " Catalogue of the Ophiurans " published in 1915 H. L. 

 Clark has not maintained the division proposed by Verrill separating 

 Ophiobyrsa and Ophiobyrsella on the basis of the characters of the 

 tooth papillae, though Matsumoto has accepted the distinctness of 

 the two genera. 



