CLARK : THE CTDARTDAE. 201 



found, were very different from those of D. papillata. While the pedicellariac of 

 bartletti are much too variable to be used as the basis for a genus, the abactiual 

 system of that species is so noticeably and constantly different from papillata 

 that I think the genus Tretocidaris may well be recognized. There are eight 

 other species of Dorocidaris which fall into the same group. It is a much more 

 natural and better differentiated genus than Stereocidaris, which has been quite 

 generally recognized in the last decade. The species of Tretocidaris are widely 

 distributed, occurring in the North Atlantic, the Caribbean and Mediterranean 

 Seas, the Gulf of Panama, northward along the Mexican coast, among the 

 Hawaiian Islands, along the Japanese coast, southward into the East Indies and 

 as far west as Ceylon. I have not attempted to determine whether any extinct 

 species are to be referred to this genus or not. The following key is based on the 

 examination of 938 specimens, representing all of the species recognized except 

 tiara. 



Key to the Species. 



Test very high, .75-.85 h. d. ; ambulacra very broad, .33-.S7 of interam- 

 bulacra, with median line bare; primaries with 8 longitudinal ridges 

 (not notched or granular), pale pink at base, olive-green near tip . . tiara 

 Test more flattened, generally less than .70 h.d. ; ambulacra generally less 

 than .33 of interambulacra. 

 Median ambulacral and interambulacral areas bare along vertical sutural 

 line; coronal plates 6-8. 

 Test moderately flattened or high, .50-70 h. d. ; actinostome moderate, 

 .35-.45 h. d. ; median interambulacral area .25 or more of inter- 

 ambulacrum in width, with several series of miliary tubereles 

 on eaeh coronal plate between scrobicular circle and vertical 

 suture; abactinal system fairly well covered with tubercles; 

 primaries 1.25-2.50 h.d.; West Indian. 

 Abactinal system large, .45-.55 h. d. ; areolae at least actinally well- 

 sunken ; primaries seldom cross-banded, usually terete, with 

 longitudinal series of numerous minute prickles but never 



thorny affinis 



Abactinal system small, .40-.45 h. d. ; areolae very shallow; prima- 

 ries prettily cross-banded with reddish (or purplish) and yellow- 

 ish (or greenish), sometimes cylindrical, often terete, frequently 

 flaring at tip, not uncommonly flattened at base, with longitud- 

 inal series of rather coarse teeth and often more or less thorny . bartletti 

 Test much flattened, .45-55 h. d. ; actinostome large (.40-50 h. d.) ; 

 median interambulacral area .20 of interambulacrum, with only 

 1 or 2 incomplete series of miliary tubercles on inner end of coro- 

 nal plates ; genital and ocular plates with margins free from 

 miliaries ; Eastern Pacific. 

 Primaries reddish, very slender, 1-1.50 h. d. ; thickness of spine about 

 6 or 7% of length; covered with 14-15 longitudinal series of 

 low, rounded granules ; collar and secondaries dark, uniform, 

 brownish-red ; no tridentate pedicellariae panamensis 



