36 PEOF. p. M. dtjkcan's revision of the 



Apical system central, large. 



Ambulacra straight, moderately broad ; poriferous zones de- 

 pressed, pairs incompletely biserial ; plates low, primaries nu- 

 merous. Interporiferous area narrow, granular, and with a 

 vertical row of small plain tubercles, placed near each poriferous 

 zone. 



Interradia with numerous very large crenulate and perforate 

 primary tubercles, in scrobicules, separated by a narrow median 

 zone with few miliaries ; there are four vertical rows of tubercle- 

 bearing plates as far as the ambitus, diminishing thence to 

 the apex by two. The plates are numerous, in vertical suc- 

 cession (16), 



Peristome ? 



Spines narrow, elongate, subcylindrical, keeled. 



Fossil. Cretaceous : Europe. 



This is a very suggestive, but at the same time, on account of 

 the defective anatomical details, a most unsatisfactory genus. 



The resemblance to Astropyga and the very non-Cidaridean 

 characters of the ambulacra render the classification merely 

 provisional. (See Astropyga, p. 78.) 



Order 11. DIADEMATOIDA (p. 24). 



It is impossible to proceed with the classification of the next 

 important group of genera of this Order without some remarks 

 concerning the anatomical characters of the Streptosomata and 

 the method of classifying the Family Diadematidse of the Stereo- 

 somata. The late Dr. S. P. Woodward described a flexible 

 Echinoid from the Chalk in 1863, and the knowledge regarding the 

 recent forms commenced with Grube, who A.eBcriibeA. Asthenosoma 

 in 1868. Then the dredgings of H.M.S. ' Porcupine ' revealed to 

 the late Sir Wy. Thomson the extraordinary spectacle of a panting, 

 plate-moving form, which he called Galveria. The descriptions 

 of the species, which turned out to belong to Asthenosoma, were 

 published in the Phil. Trans. 1874, and illustrated. The impor- 

 tance of the "imbrication" of the plates was inculcated, and the 

 bearing of this structure upon the classification of the Eamily, and 

 upon the possible alliances with the Perischoechinidse, was rather 

 overstrained. Unfortunately the very arduous life and necessary 



