112 PSEUDODIADEMA. 



ment of the tubercles of the ambulacra, which maintain their size throughout, whilst in 

 Pseudodiadema Mooreii the ambulacral tubercles are fewer in number, and more rudi- 

 mentary in size, in all the upper part of the areas. The contour of the test, moreover, does 

 not assume the pentagonal outline of Pseudodiadema depressum, nor has the upper surface 

 of the inter-ambulacral areas the median depression seen on the test of the latter. The 

 mouth opening is larger, and the decagonal lobes are more equal in size in Pseudo- 

 diadema Mooreii than in Pseudodiadema depressum. 



Locality and Strati graphical position. — I have collected Pseudodiadema Mooreii in 

 the Upper Lias of Gloucestershire. Mr. Moore found it in the same stratum near 

 Ilminster, with Ammonites communis, Sow., and Ammonites serpentinus, Schloth. Prof. 

 Deslongchamps has communicated a specimen of this urchin, which he found in the Lias 

 superieur de May, Calvados, associated with Leptcena Davidsonii, Deslong., Thecidium 

 Bouchardii, Davidson, and several other species of Upper Lias Mollusca. 



I dedicate this species to Mr. Charles Moore, of Bath, whose assiduous practical 

 researches in palaeontology have brought to light so many interesting forms from the 

 Middle and Upper Lias beds of Somersetshire. 



B. Species from the Inferior Oolite. 



Pseudodiadema depressum, Agassiz. PL VI, fig. 2 a, b, c, d, e,fg, h. 



Diadema depressum. Agassiz and Desor, Catalogue raisonne des Echinides, 



Annales des Sciences Naturelles, torn, vi, p. 349, 3 me serie. 



— — Cotteau, Etudes sur Echinides Fossiles, pi. 2, p. 43. 



— — D'Orbigny, Prodrome de Pale'ontologie, tome i, p. 290, 



No. 512. 



— — Morris, British Fossils, 2d edit., 1854, p. 76. 



— Wright, Annals and Magazine of Natural History, 2d ser., 



vol. viii, p. 258, pi. 12, fig. 2 a, b, c, d. 

 Pseudodiadema depressum. Desor, Synopsis des Echinides Fossiles, p. 65. 



Test pentagonal, depressed ; ambulacral areas convex and prominent ; inter-ambulacral 

 areas flattened ; two rows of nearly equal-sized primary tubercles in both areas ; no 

 secondary tubercles ; mouth large and decagonal ; peristome nearly equally lobed. 



Dimensions. — Height, eleven twentieths of an inch ; breadth, one inch and three 

 tenths. 



Description. — The ambulacral areas of this urchin are rather more than one half the 

 breadth of the inter-ambulacral areas, and have from ten to twelve pairs of well-developed 

 primary tubercles, separated by a zigzag line of small granulations (fig. 2 d). The inter- 



