SEA-f'RCHIXS. 



167 



In the family Akbaciid.e the median inteiainhuhicial spaces sliow as so many 

 bare bands, and the structure of tlie jaws, teeth, auricles, and spines, is intermediate 

 between the Cidarida; and Ecliinidte. The species are few. A. jm.nctulata occurs 

 upon the eastern, and ^-1. nigra upon tlie western coast of this country. In Cvelopleurus 

 the spines of the primary tubercles are immense, three times as long as the diameter 

 of the test, and tajjer gradually to a fine 

 ]ioint. One species occurs on the coast 

 of Florida. 



The Salenid^*; are a small tribe witli 

 spines like those of tlie Cidaridie in struc- 

 ture; and with the anal and genital 

 plates soldered together. Salenia uuri- 

 spina is quite common in the Caribbean 

 Sea at depths from three hundred and 

 fifty to one thousand six hundred and 

 seventy-fi\e fathoms. This species has 

 a small pui-ple body and long white ser- 

 rated spines, and in appearance resem- 

 bles Dorocklarls. The character whicli 

 removes it into another family seems a 

 very small one, yet is one in which it 

 differs from all regular sea-urchins, ex- 

 cept its own immediate relatives, which, 

 so far as we know, commenced to live 

 upon this earth in Jurassic times, and 

 have continued through cretaceous and 

 tertiary to the present day. Instead 

 I if having five ocular and five genital 

 )ilates in its rosette, this little urchin has 

 eleven, the additional one large, cres- 

 cent-shaped, and occupying a central 

 jiosition. This plate thrusts the anus 

 quite out of the centre of the rosette. 



In the DiADEMATiD^ tlie spines are 

 iidllow, long, and set with rings or ver- 

 ticillations. The test is thin, and the 

 spines delicate, so tliat it is very diffi- 

 cult to preserve a specimen entire. D. 

 iiibxicanus occurs on the west coast of 

 -Mexico, while D. setosum is found in 

 both oceans. In Echinothrix the test is stouter than in Diadema, and there are many 

 \ertical rows of very small tubercles instead of the larger tubercles of uniform size 

 which characterize Diadema and Astropyya. E. desorii of the Pacific and Red Sea 

 attains a diameter of alwut five inches, while the spines do not exceed half the 

 diameter of the test, and are often banded with gi'eenish yellow. 



In Astropyga the test is so thin as to be more or less flexil)le, and is greatly de- 

 pressed, the height usually not exceeding one-third, or even one-fourth of tlie diameter. 

 In life the colors are very bright, the ambulacral jjlates have pits or depressions of a 



:/, enlarged. 



