ASTROPYGA. 417 



eter of the test, and sometimes surpassing it. The verticillations are so 

 close and regular that externally the spines appear longitudinally striated. 

 They are generally of uniform dark color, though they are not unfrequently 

 found light-colored with transverse bands of purplish-brown and all inter- 

 mediate stages. Formerly I was led to separate this species as a distinct 

 subgenus, Garelia of Gray, on account of the peculiar structure of the spines 

 and the nature of the abactinal system. A better series of E. Desorii and 

 E. calamaris show that in this genus the structure of the spines and the 

 general aspect of the abactinal system are subject to extreme variations in 

 both the other species, fully as great as those which serve to distinguish 

 Garelia from Echinothrix. According to Stimpson, the color of spines when 

 alive is of a purplish-black color, with five blue semicircular rays on the test 

 among the bases of the spines. 



The name " turcarum " has been applied to species of Diadema as well as 

 to species of Echinothrix ; to the latter, however, it seems properly to belong, 

 though it is frequently impossible from the figures quoted to have any cer- 

 tainty of the genus to which the species belong. 



Sandwich Islands ; Fecjee Islands ; Japan ; East India Islands ; Red Sea ; Zanzibar. 



ASTROPYGA. 



Astropyga Gray, 1825, Ann. Phil. 



The test of Astropyga is so thin, and the plates so loosely connected, that 

 the whole test is more or less flexible. The test is greatly depressed. In- 

 terambulacra sunken frequently far below the bulging ambulacra near the 

 abactinal pole. Bare median interambulacral space forking, but each plate 

 having a deep pit brilliantly colored in life (Peters). The color is frequently 

 retained in alcoholic specimens. Tubercles of both areas identical in struc- 

 ture, perforate, crenulate, arranged in many vertical rows in the interam- 

 bulacra, in two in the ambulacra. The spines are shorter than in Diadema, 

 rarely attaining half the diameter of the test in length. The poriferous 



