SOME WEST INDIAN ECHINOIDS. 6 



the ambulacra arc thus more in accordance with Chark's description (wliich is, 

 however, made from a specimen 61 mm. in diameter); here the interporiferous zone 

 is also a little more than half the width of the whole ambulacrum, whereas in the 

 larger specimen it does not exceed half that width. The pores are not yoked; the 

 partition wall is rather broad, somewhat elevated; the part of the plate above 

 the pore pair is slightly elevated (Plate 16, fig. 14). The poriferous zone is dis- 

 tinctlv sunken in the larger specimen, less so in the smaller one; Clark's statement, 

 "poriferous zone scarcely at all sunken," thus does not liold for the species. The 

 number of ambulacral plates is unusually large (see above); 17-19 ambulacra! 

 plates correspond to one interambulacral plate toward the abactinal side in the 

 larger specimen, 1.5-16 in the smaller specimen. 



The interambulacra are described by Clark as having the "median interambu- 

 lacral area not at all sunken, covered with numerous miliaries and with more 

 or less horizontal grooves or narrow furrows, such as occur in Tewnocidaris." The 

 specimens before me do not agree with tliis. The median part of tlie area is dis- 

 tinctly sunken, especially in the larger specimen; the horizontal furrows across the 

 inner part of the plates are verj' distinct, especially in the larger specimen; they are 

 quite similar to those found in Cidaris cidaiis {Dorocidaris papilhfa), onlj' some- 

 what more regular (Plate 14, fig. 5, to compare ^\^th Plate 14, fig. 1, of Prouho's 

 Recherches surle Dorocidaris papillata). The expression, "such as occur in Tem- 

 nocidaris," is less fortunate, as there is no trace of the peculiar pits so character- 

 istic of Temnocidans, and it is much more natural to compare this feature in C. 

 micans with the cpiite similar structure found in the more nearly related Cidaris 

 cidaris. The areoles are not very deep; only the two lowermost are confluent, all 

 the others being distinctly separated by a wall with tubercles, narrow below, 

 gradually becoming broader toward the abactinal side. The tubercles surrounding 

 the areoles are somewhat larger than those outside; the rest of the plates is covered 

 by smaller, not verj" closely set, secondary tubercles. There is no distinct bare 

 median space. 



The apical system is essentially as in Cidaris. In the specimen figured by Clark 

 all the ocular plates are in contact with the anal area; in the larger specimen 

 before me only two ocular plates are in contact with the anal area, in the smaller 

 specimen all are widely excluded. The anal area is covered mainly by two circlets 

 of plates, an outer, larger, and an inner, smaller, within which some quite small 

 ones are found around tlic anal opening. In the smaller specimen the whole apical 

 system, in the larger only the anal area, is considerably elevated. The genital open- 

 ings are rather distant from the edge, small — perhaps both specimens are males. 

 The whole apical system is rather closely tuberculated. 



The peristome has 16-17 ambulacral plates in each scries; those of each two 

 neighboring series do not join within, so that the interambulacral plates contmue 

 alniost to the very edge of the mouth. The latter bear comparatively few tubercles, 

 the peristome being somewhat sparsely covered with spines. In the smaller speci- 

 men there are only 13-14 peristoinial ambulacral plates in each series, and the inter- 

 ambulacral plates do not reach the edge of the mouth. 



The radioles are, as described in the Ingolf Echinoidea and by Clark, very 

 characteristic; smooth, as if polished." They are rather fragile, almost all of them 



a For section, compare Ingolf Echinoidea., pt. 1, pi. 11, fig. 24. 



