310 HAWAIIAN AND OTHER PACIFIC ECHINI. 



difference in the genital pores is a sexual one. So far as could be determined 

 from alcoholic material, which is not very well adapted to such an examination, 

 there is no difference between the reproductive organs of the two species. 



The "Albatross" took depressus at the following five stations, at all of which 

 sculptus also occurred; a fact which certainly adds weight to the view that the 

 two forms are simply sexes of the same species. If the two species really are 

 distinct, their occurrence at the same stations is very interesting as tending to 

 show that Echini, like ophiurans, 1 do not follow "Jordan's law." 



Station 3818. Off Diamond Head, Oahu, Hawaiian Islands, Bott. temp. 

 44.3. 293-295 fathoms. Fne. co. s., bl. sp. 



Station 4028. Off Ukula Point, Kauai, H. I. Bott. temp. 40. 444-478 

 fathoms. Gy. s., glob. 



Station 4083. Off Kawaihae Light, Hawaii, H. I. Bott. temp. 38.7. 

 670-697 fathoms. Gy. m., for. 



Station 4086. Off Puniawa Point, Maui, H. I. Bott. temp. 44.6. 283- 

 308 fathoms. S., sh. 



Station 4088. Off Mokuhooniki Islet, Pailolo Channel, H. I. Bott. temp. 

 43.8. 297-306 fathoms. Fne. gy. s. 



Bathymetrical range, 283-697 fathoms. Extremes of temperature, 44.6- 

 38.7. 



Forty-five specimens. 



OPECHINTJS. 



Desor, 1855. Syn. Ech. Foss., p. 107. 

 Type-species, Temnopkurus costatus d'Archiac et Haime, 1853. Anim. Foss. de 1'Inde, p. 204. 



There seems to be no escape from the fact, unfortunate as it may be, that the 

 type of this genus was fixed by Pomel. Since he removed all of Desor's six 

 species except costatus from Opechinus, and since he was clearly acting within 

 his rights as first reviser, it is hard to see how any species except costatus can be 

 the genotype. It is by no means certain that the two recent species from the 

 East Indian region, referred to Opechinus by Mortensen, are really congeneric 

 with costatus, but in order that the difficulties of the problem be not increased 

 it is proposed to let the genus stand as Mortensen left it, so far as the recent 

 species are concerned. The two species may be distinguished as follows: 



Each horizontal interambulacral suture in mid-zone, with 4 large shallow depressions; a 



distinct suranal plate distinguishable on periproct variabilis. 



Each horizontal interambulacral suture in mid-zone, with 6 large, shallow depressions; 



no distinct suranal plate spectabilis. 



'See Clark, H. L., 1911, Bull. 75, U. S. N. M., p. 22-23. 



