56 DIPLOCIDARIS. 



Genus 3— DIPLOCIDARIS,* Desor. 



The genus Diplocidaris is formed of large urchins, which have all the characters of 

 the true Cidaris, but differ from them only in one particular, in having the pores in 

 the zones so arranged as to form double rows, or double oblique pairs, every third pair 

 being vertically above the third pair below them ; whereas in the genus Cidaris the pores 

 are strictly unigeminal throughout. This important modification in the structure of the 

 poriferous zones has corresponding relations with the number and disposition of the 

 tubular suckers, and probably with the function of respiration. The ambulacral areas are 

 narrow, straight, and flexed, with two rows of small marginal granules ; the inter-ambulacral 

 areas are wide ; the areolas are round or elliptical, and the bosses have deeply crenulated 

 summits ; the tubercles are of moderate size ; the miliary zones are very wide, and the 

 surface of the plates is covered with large well-defined granules, set at some distance from 

 each other. 



" The spines are short, massive, and cylindrical ; their surface is covered with granules, 

 or pustules, instead of spines as in Rabdocidaris." — Desor. 



All the species known have been found in the Oolitic rocks. 



A. Species from the Upper Lias ? 

 Diplocidaris Desori, Wright, nov. sp. PI. VIII, fig. 5. 



Test large, form unknown ; ambulacral areas narrow and slightly flexed, with two 

 rows of small marginal granules ; poriferous zones follow the flexures of the area ; the pores 

 round, and contiguous, the septum as thick as the diameter of the pore, with a prominent 

 tubercle on its surface ; every two pairs of pores are set obliquely to each other, so that 

 the pores of every third pair stand vertically over each other ; inter-ambulacral plates large, 

 rhomboidal, as deep as they are broad ; areola large, circular ; scrobicular circle complete, 

 abutting against the poriferous zones ; granules of the circle of the same size as those 

 covering the rest of the plate ; areola shallow, boss not prominent, tubercle small ; miliary 

 zone wide, with four or six rows of well-spaced-out granules. 



The fragment which I have figured was kindly communicated by my friend, 

 Mr. S. P. Woodward ; it was collected near Yeovil, from a rock supposed to be Inferior 

 Oolite. 



It is very interesting to find this fragment of a Diplocidaris so far down in the Oolitic 

 series, as the specimens of this genus hitherto discovered have all been found in the Coral 



* From hnrXovi, double. 



