70 CIDARIS 



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

 rather less so than in C. subvedcfdosa ; 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 obhquely ; there are eighteen pores (thirty-six 

 in all) 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 

 surrounded by an undercut overhanging border, encircled by a series of about twenty 

 granules, each raised on a distinct shield-like mammillated 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 vdth 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 sutures ; 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. 



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

 closely approaches C. sceptrifera and C. sttbvesiculosa ; it differs from the foi-mcr 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 



