234 Dr. T. Wright on the Paleontology of the Isle of Wight. 



miliary eminences are small, their summits are deeply crenulated, 

 and the tubercles, of proportional size, are deeply perforated; at the 

 circumference six rows of granules separate the tubercles from each 

 other, but towards the upper surface the four central rows are 

 absent, which leaves a naked space in the middle of the area ; 

 three rows of granules in like manner separate the tubercles 

 from the poriferous valleys ; at the base of the area, and extend- 

 ing as far as the circumference of the test, are incomplete rows 

 of secondary tubercles ; these gradually diminish in size and dis- 

 appear at the upper surface, which is occupied with an unequal- 

 sized, close-set granulation about three rows deep ; the ambu- 

 lacral areas are one-third narrower than the interambulacral, 

 they are however very prominent and convex, and are occupied 

 with two rows of primary tubercles about ten in a row ; the lower 

 six pairs of tubercles are nearly as large as the corresponding 

 tubercles in the interambulacral areas, but the upper four pairs 

 are much smaller, so that whilst there is a great uniformity in 

 the size and form of the tubercles on the base and circumference 

 of the test, there is a very marked difference between those of 

 the ambulacra and those of the interambulacra in the vicinity of 

 the ovarial disc ; the intertubercular space is occupied by a zig- 

 zag band of granulation, which is narrow below where the tu- 

 bercles are large, but becomes broader above where they are 

 small. The pores are arranged in double pairs near the summit 

 and mouth, but in the other part of the avenues they are in 

 single pairs ; the apical disc is absent in our specimen, and the 

 mouth is large and decagonal. 



Affinities and differences. — This species nearly resembles D. 

 Bourgueti, Ag., but differs from it in the rudimentary condition 

 of the upper tubercles of the ambulacra, and in having the pores 

 in double pairs above and below ; the intermediate granulation is 

 likewise less homogeneous than in D. Bourgueti. 



Locality. — I collected this Urchin from the lower greensand at 

 Atherfield, in No. 4 of the Cracker group of Dr. Fitton's section : 

 it must be very rare, as none of the cabinets of Atherfield fossils 

 hitherto examined by me contain a specimen of this Diadema. 

 It has been collected by M. Cotteau from the Neocomien stage 

 at Auxerre, where it is likewise very rare. 



History. — Discovered by the author in the Isle of Wight in 

 1850, and by M. Cotteau in France in 1851, but first described by 

 the latter in his * Catalogue Methodique des Echinides recueillis 

 dans Fetage Neocomien/ and which brochure I received since 

 I read this communication. As there is no figure of this Urchin 

 extant, I intend giving one of the beautiful specimen before 

 me, along with some other new forms of that group which I hope 

 shortly to publish. 



