23 Mr. H. Seeley on Cambridge Palceontology : — 



Cidaris gradata. 



Greatly inflated, flattened below, with the peristome circular ; ele- 

 vated above, with the periprocte pentagonal. Arabulacral areas 

 nearly one-third of the width of the interambulacrals, sinuous, 

 and divided into two parts by a deep mesial groove ; furnished 

 with four rows of rather large granules, which are not arranged 

 in straight transverse lines. Poriferous zones deeply im- 

 pressed on the base, furnished with a close row of granules, 

 which are rather smaller than those of the intermediate spaces ; 

 they divide the pairs of pores. The ambulacra are narrow at 

 the apex, so that the inner rows of granules are suppressed ; 

 they become a little narrower towards the mouth. Inter- 

 anibulacral area with two rows of rather convex plates, of 

 three and four each. The tubercles are small on the base, 

 and progressively increase in size, so that the scrobiculse of 

 the uppermost of the 'three-series' occupies half the width of 

 the area. The uppermost plate of the ' four-series ' is small 

 and granulated, or has only a rudimentary tubercle. The 

 areolae are circular, moderately impressed, placed below the 

 middle of the plates ; margined by two rows of large granules 

 of about thirteen each, an inner row forming the margin of 

 the pit, and an outer row between these, which does not reach 

 to the margin ; thus both rows appear to form one irregular 

 circle. The bosses are truncated cones, which are propor- 

 tionally elevated inversely to their size. The tubercles are 

 large depressed spheres. Miliary granulation coarse, on the 

 upper part very large, so that a line of not more than twelve 

 would be sufficient to reach across the widest part of the 

 largest plate. 



Nearly \ inch high, more than | inch wide ; oral aperture f inch, 

 apical aperture -^-^ inch. 



Differs from C. Heberti (Desor) in wanting the character 

 " scrobicules petits et serres ;" from C. dissimilis (Forbes) in the 

 more elevated form, four rows of ambulacral granules, wide 

 ambulacra, &c. 



It is common, perhaps commoner than C. Sedgwickii, but in 

 general only occurs in detached plates. A single beautifully 

 perfect example is preserved in the cabinet of J. Carter, Esq. 



Cidaris Sedgwickii. 



Inflated, elevated [rather subconical ?] . The ambulacral areas 

 are narrow and sinuous. The poriferous zones much im- 

 pressed, and rather narrower than half the intermediate taper- 

 ing space ; they have a row of granules down the middle, 

 separating the two rows of pores : towards the apex the gra- 



