134 HAWAIIAN AND OTHER PACIFIC ECHINI. 



opinion (1907, Ingolf Ech., pt. 2, p. 96) that the two genera are nearly related. 

 He thinks the character of the pedicellariae indicates relationship and to a certain 

 extent this is true but it must be borne in mind that these pedicellariae are of 

 a generalized type and are not at all distinctive. It is, however, worthy of note 

 that ophicephalous pedicellariae are lacking in both genera. 



Key to the Genera of Aeropsidae. 



Test elongate, more or less cylindrical; mouth flush with ventral surface; ambulacrum III 



not depressed dorsally Aeropsis. 



Test wide and flattened; mouth vertical; ambulacrum III greatly enlarged and depressed 



dorsally "• Aceste. 



Aeropsis. 



Mortensen, 1907. Ingolf Ech., pt. 2, p. 90. 

 Type, Aerope rostrata Norman, 1876. Proc. Roy. Soc. London, 25, p. 212. 



Mortensen's alteration of the preoccupied name Aerope to Aeropsis was 

 a happy solution of the difficulty and will no doubt meet with general accep- 

 tance. The number of species in the genus is still uncertain owing to lack 

 of material. That there is one species in the North Atlantic seems fairly certain 

 but whether there are two or three species in the Indo-Pacific region or only 

 one is not so clear. There is a possibility as Mortensen suggests that the speci- 

 men taken by the Challenger in the Arafura Sea was not the same as the 

 Panamic species. Koehler's A. sibogae from the East Indies is based on the 

 specimens which de Meijere identified as fulva and I am obliged to consider 

 de Meijere's identification correct. Koehler naturally lays stress on the differ- 

 ence between the rostrate pedicellariae which he found and the one which Mor- 

 tensen figures for fulva, but Mortensen only found a single specimen and it is 

 possible that it was merely a peculiar tridentate. I am inclined to this view 

 because of the fact that in none of the six specimens herein recorded as fulva 

 are there any pedicellariae like Mortensen's figure. I am not willing to accept 

 sibogae as different from fulva on the strength of this one peculiar pedicellaria, 

 and therefore treat Koehler's name as a synonym. There are no other tan- 

 gible differences between the Siboga and the Albatross specimens. By an 

 unfortunate lapsus calami on the legend of Koehler's plate II (1914. Ech. Indian 

 Mus. Spat.) the Siboga specimen is called Aeropsis urbcri and the same error 

 occurs in the explanation of the plate on p. 242. 



