16 BULLETIN 74, UNITED STATES NATIONAL MUSEUM. 



but the material at my disposal is far from sufficient to decide that, especially in 

 view of tiie fact that some specimens of the variety have the radicles as stout as 

 those of the typical form. A close examination of a large series of these forms 

 will be necessary to decide the question; for the present, however, it seems to me 

 necessary to keep the variety distinct from the typical form. 



CIDARIS RUGOSA (H. L. Clark). 

 Plate 14, fig. 11; plate 10, fig. 1. 

 DoTocidaris rugnsa H. L. Clark, The ("idaridoe, ]>. 210, pKs. 4-.5, pi. 7, fig?. 5-8. 



The most conspicuous difference from C. cidaria (papiUata) is evidently the 

 more closely tubcrculalcd median ambulacral area. Whereas in G. cidaris there is, 

 even in very large specimens, only one secondary tubercle within the primary one, 

 placed almost in the middle of the plate," there are in C. rugosa generally two sec- 

 ondary tubercles on each plate, the result being that the median space is wholly 

 covered with tubercles, whereas in C. cidaris it is comparatively open (Plate 14, fig. 

 1 1 to compare with fig. 12). The median space is also conspicuously narrower in 0. 

 rugosa than in G. cidaris, as shown in the two figures cited, which have been drawn 

 from equal sized specimens of the two species. 



That the median interainbulacral space is broader in G. rugosa than in G. cidaris, 

 as stated by Clark, seems to me to be scarcely a constant feature; but there 

 is another distinguishing character in the interambulacra not mentioned by Clark, 

 namely, that the tubercles around the areoles are more prominent than in G. cidaris 

 (compare Clark's figs. 7 and S, Plate 7). That the abactinal sj'stem is more uni- 

 formly tuberculated in G. rugosa than in G. cidaris does, at least, not hold good in 

 the single s])ecimen at my disposal. 



The radicles are stated by Clark to be twice to two and one-half times the 

 horizontal diameter. In the specimen before me, 32 mm. horizontal diameter, the 

 longest radioles are 40 mm. Also in the specimens figured by Clark the longest 

 radicles appear to be scarcely twice the horizontal diameter. In transverse sections 

 the radicles do net differ from those of C. cidaris. 



The pedicellariffi are mainly like those of G. cidaris. The lower edge of the 

 terminal opening in the large globiferous pedicellaritc is not slit up, as is often 

 (always?) the case in G. cidaris. The tridentate pedicellarije (Plate 16, fig. 1) are 

 slightly broader than in that species. In this species also one may find transitional 

 foi-ms between the tridentate and the small globiferous pedicellarise. 



In the place cited in The Cidaridje, Clark mentions that I have identified 

 seven specimens of this species in the U. S. National Museum as "Dorocidaris 

 papillata" and another one as "Stcreocidaris ingolfiana" ; on page 190 it is stated 

 that I have identified a series of remarkably short-spined specimens of "Phyllacan- 

 thus baculosa" from Aden as "Gidaris metularia." "As M. did not clean an ambu- 

 lacrum, it is not strange that he failed to see the very characteristic poriferous 

 zones. But it is hard to understand how he overlooked the conspicuous purple 

 spots on the cellar of the spines." I am not going to defend my identifications cf 



a In younger specimens of Crirlaris, up to about 30 mm. horizontal diameter, the inner tubercle ie 

 developed only on one nide, irregularly alternating. 



