ECHINODERMATA. 



35 



It is distinguished from Cidaris Edwardsii by the width of the poriferous zones, and 

 the thickness of the septum which separates the pores composing a pair ; by the circular 

 form of the areas, and the complete scrobicular circle of granules that surround and 

 limit them in Cidaris Fowleri : whereas in Cidaris Edwardsii the areolas are oblong and 

 confluent. In the structure of the spines there are likewise important differences. 

 Compare PI. I, fig. I /, with fig. 4 d. 



Cidaris Fowleri is distinguished from Cidaris Bouchardii (PI. I, fig. 2 a, b, and PI. VIII, 

 fig. 3 a, b, c), which occurs with it in the same bed, by the latter being in general a rather 

 more depressed form, its ambulacral areas having only two marginal rows of granules ; 

 the poriferous zones being much narrower, and the areolas of the primary tubercles 

 more deeply sunk in the plates ; the tubercles themselves are larger, the scrobi- 

 cular circle is more prominent, and the granulations in the miliary zone are fewer and 

 larger. 



Cidaris Fowleri differs from Cidaris Wrightii (PI. I, fig. 3), which is likewise found 

 rarely in the Pea Grit, by the latter having a very thick test, large primary tubercles, with 

 very small perforations ; the poriferous zones are narrow, and the ambulacral areas have 

 only two rows of marginal granules (fig. 3 c). Moreover, it is a much smaller and a more 

 inflated form than Cidaris Fowleri. 



Only one tubercular plate of Cidaris Ilminsterensis from the Upper Lias (PI. V, 

 fig. 6 a, b) is known ; but so finely are the specific characters defined upon that fragment, 

 that we are enabled to point out the differences between these two species, so nearly 

 related to each other in time. In Cidaris Ilminsterensis the scrobicular circle of granules 

 abuts very close upon the poriferous zones, which are narrow, and have the pores placed 

 close together; whereas in Cidaris Foioleri there is a considerable granulated space 

 between the scrobicular circle and the poriferous zones, which are wide, and have their 

 pores placed far asunder. 



Locality and Stratigraphical position. — Cidaris Fowleri was obtained from the Pea- 

 grit of the Inferior Oolite at Crickley Hill, Gloucestershire. It has been likewise found 

 in the same bed at Birdlip and Leckhampton Hills. The remarkable rock in which 

 these Cidarites are found seems to have been a tranquil littoral deposit in shallow water, 

 as the most of the Echinoderms are finely preserved, with all the sharpness of their 

 sculpture quite intact. Associated with this urchin are — 



Cidaris Bouchardii, Wright 

 Cidaris Wrightii, Desor 

 Diadema depressum, Agassiz 

 Echinus germinans, Phillips 

 Polycyphus Beslongchampsii, Wright 



Ilemipedina BaJceri, Wright 

 Hem ipedina perforata, Wrigh t 

 Ilemipedina tetragramma, Wright 

 Ilemipedina Waterhousei, Wright 

 Ilemipedina Bonei, Wright 



