colcboc;::,*th()tus ateatus. 425 



delicate miliaries, irregularly scattered between the arcs of the porif- 

 erous zone. In the interambulacral spaces the tubercles are not arranged 

 in vertical rows, but form irregular horizontal rows, — sometimes two on each 

 plate ; they are largest near the ambitus, and quite small on the actinal sur- 

 face in the small interambulacral field left between the broad petaloid ex- 

 pansions of the poriferous zone. These interambulacral tubercles are not 

 uniform in size, nor do they diminish towards the abactinal pole, but are 

 irregularly arranged, as far as size is concerned, over the whole inter- 

 ambulacral zone above the ambitus. Actinostome large, pentagonal, with 

 but slight cuts and short lips slightly prominent. The miliaries of the upper 

 part of the test are regularly arranged round the base of the primary 

 tubercles. 



The usual coloring of the spines of this species is of a dark-violet, almost 

 black, though there are a few specimens of a greenish tint with olive-green 

 colored spines, which have been distinguished as a separate species (P. pedi- 

 fera) : they are said to come from Valparaiso and Chili ; but as thus far there 

 is no positive authority for their having been collected there, the locality of 

 Chili and the west coast of South America can be accepted only provisionally. 

 The original specimens of Blainville came from Oahu, and the series I have 

 had occasion to examine does not show any features, except color, by which 

 P. pedifera could be separated from C. atrata. 



The test is thick, flattened on the actinal side, somewhat conical, with 

 swollen edges near the ambitus, in }'oung specimens becoming quite gibbous, 

 and frequently almost rectangular in outline from above as well as in profile, 

 owing to the flattening of the abactinal part of the test ; buccal membrane 

 only strengthened by few irregular plates in the continuation of the ambu- 

 lacra. The ten buccal plates carry small prominent club-shaped spines. 



75. largest specimen seen. 

 Zanzibar ; Java ; Sandwich Islands. 



