FROM THE LOWER GREENSAND. 91 



four pairs are much smaller, so that, whilst thei-e 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 narrow 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). 



Ajfinities and Differences. — Psciidodiadema Fitloni nearly resembles P. Bour(/ueti, Ag., 

 but diflers 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 Slrafiffraphlcal Position. — I collected this Urchin from the Lower Green- 

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

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

 specimen. 



History. — I discovered this fossil in IS 50, 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 Atherfiekl section and the strata below 

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



PsEUDODiADEMA Malbosi, Agassiz 8^' Desor. PI. XX, figs. 1, a—f. 



Diadema Malbosi, Agassi: and Besor. Catal. r.iis. des Eehinides, Ann. Science. 



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



— — B'Orhignij. Prodrome de Paleont. strat., t. ii, p. 201, 



1850. 

 DiPLOPOBiA — Desor. Synops. des Eehinides fossiles, p. 7S, pi. xii, figs. 



12—14, 1856. 

 — — Leymerie et Cotteau. Cafnl. tics Ecbinid. Foss. des 



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



p. 324, 1850. 

 DiAUEMA Mackesoxi, Forbes. Woodward's Notes on British fossil Diadems, 



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



— Mackiei, TJ'oodward. Ibid. 



— Malbosi, Pictet. Traite de Paleont., 2" ed., t. iv, p. 245, 1857. 

 DirLOPODiA — I>'.//-c//«;c Ics Corbicrcs. Mem. Soc. Geol. de France, 2" ser., 



t. vi, p. ;!84, 185!). 



