300 HAWAIIAN AND OTHER PACIFIC ECHINI. 



ORECHINUS. 



Doderlein, 1905. Zool. Anz., XXVIII, p. 622. 

 Type-species, Trigonocidaris monolini A. Agassiz, 1879. Proc. Amer. Acad., XIV, p. 203. 



In his report on the "Siboga" Echini, de Meijere removed T. monolini from 

 Trigonocidaris and placed it in Genocidaris but it is not clear on just what 

 grounds he made the change. Doderlein has showed however that the characters 

 of both the abactinal system and buccal membrane prevent its association with 

 Genocidaris and so he established the genus Orechinus for its reception. This 

 genus is so near Trigonocidaris that it might be regarded as superfluous, but 

 the lines of development are probably a little easier to follow if the two genera 

 are retained. So far as known Orechinus is a monotypic genus confined to the 

 deep waters of the Indo-Pacific region. 



Orechinus monolini D6d. 



Trigonocidaris monolini A. Agassiz, 1879. Proc. Amer. Acad., XIV, p. 203. 

 Orechinus monolini Doderlein, 1905. Zool. Anz., XXVIII, p. 622. 



Plate 93, figs. 27-31. 



The "Challenger" took a single specimen, 8 mm. in diameter, in 520 fathoms 

 near the Kermadec Islands and the "Valdivia" also took a single, somewhat 

 larger specimen in 278 fathoms off South Africa. The "Siboga" found the 

 species fairly common, in the Dutch East Indies, taking it at ten widely scattered 

 stations in from 262 to 1 156 fathoms. These specimens ranged from 4 to 14 mm. 

 in diameter. Finally the "Albatross" found monolini not uncommon among 

 the Hawaiian Islands, and brought home a series of specimens ranging from 6 to 

 22 mm. in diameter. In spite of the larger size of some of these specimens, there 

 is little to add to the details that have been published by de Meijere and Doder- 

 lein. Globiferous pedicellarise are rare in some specimens but fairly common in 

 others; the valves (PI. 93, figs. 27, 28) are about .60 mm. long, with the base 

 .30 mm. wide and the terminal tooth about .15 mm. long. The ophicephalous 

 are common; the valves (which have been figured by Doderlein) are .20-.25 mm. 

 long, besides the loop which adds .05-. 10 more. The tridentate are always rare 

 and often wholly wanting, which is unfortunate as they are rather characteristic ; 

 the valves (PI. 93, figs. 29, 30) are .40-.70 mm. long, with the blade .12-.18 mm. 

 wide; they are strongly curved and meet only at the tip. The triphyllous are 

 rare or at least hard to find; the valves (figured by Doderlein) are about .13 mm. 



