244 bulletin: museum of compakative zoology. 



Prionechinus depressus A. Ag. and Clark. 



The specimens to whicli we have giveu this name were taken with the preced- 

 ing, but the larger individuals (those over 4 mm. in diametei") are so obviously 

 different tliat the two are easily separated. In this species, the test is very flat 

 and the bare, interambulacral grooves are very conspicuous. The abactinal sys- 

 tem is entirely different from that of P. sculjjtus, as there is very little sculptur- 

 ing, and the genital openings are situated at the extreme distal tip of the plates, 

 in a groove which is continuous with the interambulacral groove. The spines, 

 color and size are as in sculptus. While it is not impossible that this species and 

 the preceding are simply the two sexes of one species, such sexual dimorphism is 

 not at present known among the regular Echini. 



Station 3818. Off Diamond Head, Oahu, 293-295 fathoms. 

 " 4028. Off Ukula Point, Kauai, 444-478 fathoms. 

 " 4083. Off Puniawa Point, Maui, 238-253 fathoms. 

 4086. Off Puniawa Point, Maui, 283-308 fathoms. 

 4088. Off Mokuhooniki Islet, Pailolo Channel, 306-308 fathoms. 

 Forty-five specimens. 



Pleurechinus hawaiiensis A. Ac. and Clark. 



Although this species is closely allied to P. siamensis Mortensen, it differs de- 

 cidedly in color and in one or two details of structure. The abactinal interambu- 

 lacral space is not at all bare, but on the other hand there are only half as many 

 secondary and mihary tubercles on the ambulacral and interambulacral plates near 

 the ambitus, as in the specimen of siamensis figured in detail by Mortensen (1904). 

 The anal system is covered by several large plates and a few small ones, and the 

 anus is subceutral. The color of the test is prevailingly green, with the abactinal 

 intei'ambulacra lighter and often pure white in striking contrast. The primaries 

 are whitish with more or less red. The tendency towards a bright red coloration 

 is noticeable and two specimens are almost uniformly bright red, test as well as 

 spines. Around the actinostome the test often becomes whitish, while abactinally 

 it is frequently marked with purplish-brown. While the color is thus very vari- 

 able, there is no tendency to approach the coloration of siamensis, except as each 

 species has a bright red variety. 



Station 3823. Off Lae-o Ka Laau Light, Molokai, 78-222 fathoms. 

 3847. Off Lae-o Ka Laau Light, Molokai, 23-24 fathoms. 



3871. Off Mokuhooniki Islet, Auau Channel, 13-43 fathoms. 



3872. Off Mokuhooniki Islet, Auau Channel, 32-43 fathoms. 

 " 3876. Off Lahaina Light, Maui, 28-43 fathoms. 



3962. Off Laysau Island, 16 fathoms. 

 " 3978. Off Modu Mann, 32-46 fathoms. 

 4148. Off Modu Mauu, 26-33 fathoms. 

 " 4150. Off Modu Mann, 71-160 fathoms. 

 Sixteen specimens. 



