ECHINO.METRADAE. 423 



tubercles perforated. Teeth with gutter, without keel ; jaws equilateral. 

 The test is pinkish, probably darker in life, dotted with violet. The spathi- 

 form and club-shaped spines of actinal surface green. Those of abactinal 

 part of test white, with two or three violet bands. Ambulacral zones not 

 half as broad as the interambulacra, with one prominent vertical row of 

 pores on outer edge of ambulacra. The heads of the larger pedicellariaa 

 are a brilliant yellow or greenish. 



China Seas. 



ECHINOMETRADAE. 



Family Echinoinetradae Gray, 1855, Proc. Zobl. Soc. London. 



Gray first called attention to the affinities of the genera here included in 

 the Echinoinetradae, which are understood in a somewhat wider sense, and 

 include not only Echini with an oblique axis, but also the greater part of the 

 Echini included by Desor in his division of Polyporidae. From the analysis 

 of the plates of the ambulacral system, we can readily separate the Echi- 

 noinetradae from the Echinidae proper, the former having always more than 

 three pairs of pores to each arc, while in the Echinidae the arcs are always 

 composed only of three pairs. This division, although it appears a nu- 

 merical one, is yet one of great physiological importance, as the mode of 

 growth of the poriferous zone in these two families is totally unlike. 



COLOBOCENTROTUS. 



Colobocentrotus Br., 1S35, Prod. Des. An. 



The Echini of this genus do not become as large as Heterocentrotus, but 

 have like them a solid test and elongated axis lying in the same plane as 

 that of Heterocentrotus. The ambulacra are much broader than in the other 

 genera of the family, the actinal surface is flat, and the poriferous zone takes 

 consequently a great development. The tubercles are smooth, not crenulate, 

 having only an imperfectly developed mammary boss ; usually there are 

 two principal vertical rows of tubercles in the ambulacra, forming irregular 

 horizontal rows of several tubercles along the interambulacra. Arcs of 

 pores composed of as many as nine or ten pairs of pores. Actinostome 



