ECHINODERMATA. 47 



que les tests et qu'ils sont connus de tous les paleontologistes c'est a eux, et partant au test 

 decrit ci-dessiis, que je crois devoir conserver le nom primitif de Cidaris BlumenhachiH' * 



The test of Cidaris jlorigemma is round, and much inflated at the sides ; it is mode- 

 rately depressed at both poles, but is most so on the upper surface ; the ambulacral areas 

 are narrow, and nearly of a uniform breadth throughout ; they are very sinuous and pro- 

 minent, and are furnished with two rows of granules on the margins of the areas ; between 

 these, for about the length of two of the large tubercular plates, there are two rows of very 

 small granules internal to the marginal ones (PI. II, fig. 2 g) ; the marginal granules are 

 raised on small basal eminences, but the internal granules are not ; the six or eight marginal 

 pairs nearest the peristome are very much larger than those in the middle and upper parts 

 of the areas : the poriferous zones are of moderate width ; the pores forming a pair are 

 separated from each other by a septum equal in width to the diameter of a pore (fig. 2y) ; 

 there are nineteen or twenty pairs of pores opposite each of the large equatorial tubercular 

 plates ; the zones are rather deep, from the prominence of the ambulacral areas in the 

 middle, and that of the scrobicular circles external to them. 



The inter-ambulacral areas are nearly five times the width of the ambulacral areas and 

 poriferous zones ; the plates of the tubercular columns are deep, there being only from six 

 to seven plates in each column ; the areolas are large and circular, especially above, but 

 they incline towards an oval from below ; their margins are surrounded by a prominent 

 scrobicular circle of fifteen or sixteen well- spaced- out granules (fig. 2 g), each of which is 

 raised on an oval, shield-like base. In consequence of the size of the areolas in the upper 

 part of the areas, the scrobicular circles of the two uppermost pairs closely approximate ; 

 but from this point to the peristome there is a considerable inter-tubercular space, which 

 is filled up with miliary granules of different sizes ; those nearest the areolas are raised 

 on small basal elevations, which alternate with those of the scrobicular circle, and the 

 rows internal to them diminish in size as they approach the median sutural line, where 

 they become quite miliary : the mammillary bosses rise from a wide base (fig. 2 g) ; the 

 three or four lower pairs have smooth summits, and the two or three upper pairs only are 

 crenulated ; the crenulations, however, are by no means either deeply sculptured, or very 

 persistent in diSerent specimens ; the tubercles are large, and are raised on a slightly 

 contracted neck ; the perforation in the hemispherical head has the form of an oblong slit, 

 which passes through the head, and extends to the summit of the boss. 



The mouth opening is large, and the peristome has a pentagonal form (fig. 2 b). In 

 specimen b, it measures nine tenths of an inch in diameter, that of the equatorial diameter 

 being two inches and two tenths ; the primary tubercles in the vicinity of the peristome 

 are large and well developed, although smaller than those on the sides and upper sur- 

 face of the test ; the minute tubercles at the base of the ambulacral areas are only a little 

 larger than the marginal granules of these areas. 



* ' Synopsis des Echinides Fossiles,' p. 5. 



