70 CIDARIS 



poles ; the ambulacra! areas are narrow and flexuous, rather more so than in C. sceptrifera, 

 rather less so than in C. subvesicidosa ; granules six in number at the ambitus, diminishing 

 to four at the poles ; the central rows at the upper and under surfaces minute and irregular ; 

 the four central rows at the ambitus composed of granules of less size than those of the 

 exterior rows, consisting of greater numbers, and somewhat irregularly arranged ; the 

 poriferous zones are narrow and depressed, and follow the flexures of the areas ; the pores 

 are round, closely situated, and disposed obliquely ; there are eighteen pores (thirty-six 

 in aU) opposite one of the largest plates ; the interambulacral areas are very wide, 

 five to six plates in a column ; the areolas are wide, slightly oval (the minor axes being 

 towards the poles) at the ambitus, circular at the peristome and anal margins, and are 

 svu-rounded by an undercut overhanging border, encircled by a series of about twenty 

 granules, each raised on a distinct shield-like maramillated plate ; the areolas at the 

 equator have their borders separated from the upper and under plates by a small interval 

 occupied by about five sets of granules ; at the under surface these granules are absent, 

 and the scrobicular margins are in contact ; at the upper surface the granules increase in 

 number ; the penultimate plate of the anal surface has an areola rather larger than that 

 below ; the final plate has a rudimentary tubercle in a small circular areola, this last plate 

 is covered with granules ; the boss is not prominent, its summit is smooth and without 

 crenulation, the tubercle is moderately large and perforated ; the miliary zone is narrow, 

 and the granules are so arranged as to present the appearance of radiating from the 

 scrobicular margin towards the sutui'es ; they are much smaller than those surrounding 

 the areolas ; the surface on which they are studded dips towards the sutures, causing the 

 latter to be clearly defined. The apical disc is of the same size as the mouth-opening 

 and in the specimen figured is six tenths of an inch in diameter ; the plates with which 

 it is furnished are large, and covered with granules ; the mouth is furnished with strong 

 jaws, shown in the plate. 



" The spines are long, cylindrical, and very slightly tapering, covered with small, 

 strong, equal-sized granules, the points of which project outwards. They are 

 arranged in ten regular longitudinal ridges, with a sulcus between them covered with 

 a very fine granulation. The spiny granules continue to within a tenth of an inch of the 

 collar ; the neck is very short and smooth, the head moderately large, cone-shaped, and 

 longitudinally striated with numerous fine lines ; the rim of the acetabulum is very finely 

 crenulated. The length of the longest spine, that of the ambitus, is one inch and eight 

 tenths ; it is slightly broken at the extremity, and therefore would, if perfect, be rather 

 longer ; its diameter is one tenth of an inch ; the short spine, which is unbroken (seen in 

 the right hand of the plate), has its extremity suddenly expanded. 



" Affuiliies and Differences. — Cidaris intermedia, in the general appearance of its test, 

 closely approaches C. sceptrifera and C. subvesiculosa ; it differs from the former in the 

 scrobicular margins from the ambitus to the peristome being in contact, or not separated by 

 more than one granule, — in the more narrow miliary zone, — in the lesser number of rows 



