FROM THE LOWER GREENSAND. 91 



four pairs are much smaller, so that, whilst there is a great uniformity in the size and 

 form of the tubercles at the base and ambitus of the test, there is a very marked 

 difference between those of the ambulacra and inter-ambulacra in the vicinity of the apical 

 disc (fig. 1 b) ; the inter-tubercular space is occupied by a zigzag band of granulation, which 

 is naiTow below where the tubercles are large, and broader above where they are small 

 (fig. 1 e). The poriferous zones are narrow and subflexuous; and the pores arranged 

 in single pairs ; near the disc they are slightly bigeminal ; the apical disc is absent in our 

 specimen. The mouth-opening is large and the peristome slightly decagonal (fig. 1 c) . 



Affinities and Differences. — Pseiidodiadema Fittoni nearly resembles P. Pourgueti, Ag., 

 but differs from it in the rudimentary condition of the upper tubercles of the ambulacra, 

 and in having the intermediate granulation on the miliary zone less homogeneous. 



Locality and Stratigrapldcal Position. — I collected this Urchin from the Lower Green- 

 sand at Atherfield, in bed No. 4 of the Cracker group. Dr. Fitton's section ; it must be very 

 rare, as none of the cabinets of Atherfield fossils hitherto examined by me contain a 

 specimen. 



History. — I discovered this fossil in 1850, and in the first instance erroneously 

 identified it with a specimen found in France, and then briefly described by M. Cotteau 

 as Diadema Autissiodorense. The fine figures and detailed description lately published 

 by M. Cotteau in his additions to the " Paleontologie Francaise " have enabled me to 

 correct my error, and I now dedicate this species to the memory of my late friend 

 Dr. Fitton, F.R.S., whose admirable memoir on the Atherfield section and the strata below 

 the Chalk will long remain models of patient research and accurate scientific investigation. 



PsEUDODiADEMA Malbosi, Affttssiz ^' Dcsor. PL XX, figs. 1, a—f. 



DiADEM.\ Malbosi, Agassiz and Besor. Catal. rais. des Ecliinides, Ann. Science. 



Nat., 3me ser., t. vi, p. 350, 184G. 

 ^ ., — — UOrbigny. Prodrome de Paleont. strat., t. ii, p. 201, 



1850. 

 DiPLOPODiA — Desor. Synops. des Ecliinides fossiles, p. 78, pi. xii, figs; 



12—14, 1856. 

 — — Leijmerie et Cotteau. Catal. des Echinid. Toss, des 



Pyrenees, Bullet. Soc. Geol. de France, 2" ser., t. xiii, 



p. 324, 1856. 

 Diadema Mackesoni, Forbes. Woodward's Notes on British fossil Diadems, 



Mem. Geol. Surv., Decade V, 185G. 



— Mackiei, Woodward. Ibid. 



— Malbosi, Pktet. Traite de Paleont., 2' dd., t. iv, p. 245, 185". 

 DiPLOPODiA — D'^/-c///flc les Corbieres. Mem. Soc. Ge'ol. de France, 2' ser., 



t. vi, p. 384, 1859. 



