from the Lias and Oolites. 29 



uniform size around the base ; but it is readily distinguished 

 from D. depressum by the number and greater development of the 

 tubercles of the ambulacra, which maintain their size throughout ; 

 whilst in D. Moorei the ambulacral tubercles are fewer in num- 

 ber and rudimentaiy in size in all the upper part of the areas. 

 The contour of the test moreover does not assume the penta- 

 gonal outline of D. depressum, nor has the upper surface of the 

 interambulacral 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 D. Moorei than in D. depressum. 



Locality and stratigraphical range. We have collected D. 

 Moorei in the Upper Lias of Gloucestershire. Mr. Moore found 

 it in the same stratum near Ilminster with Ammonites communis 

 and A. serpentinus. Professor Deslongchamps has communicated 

 a specimen of this Urchin which he found in the Lias superieure 

 of May, Calvados, associated with Leptana Davidsoni and The- 

 cidea Bouchardii and several other species. 



We dedicate this species to Mr. Moore, of Ilminster, whose 

 assiduous researches have brought to light so many interesting 

 forms from the Upper Liassic beds of Somersetshire. 



Genus PEDINA, Agassiz. 



As this genus was incorrectly defined in our memoir on the 

 Cidaridse, it having been there stated that the mammillary emi- 

 nences were " crenulated like those of Diadema" we take this 

 opportunity of correcting the error, and giving a definition more 

 in accordance with our present knowledge. 



Test thin, circular, more or less depressed ; primary tubercles 

 small and perforated ; mammillary eminences with smooth ring- 

 like summits without crenulations ; pores in general disposed in 

 triple oblique pairs ; mouth small and slightly decagonal, mar- 

 gin not much notched ; ovarial disc small and not prominent ; 

 ambulacral areas with one, two, or more rows of small tuber- 

 cles ; interambulacral areas sometimes with two rows only, some- 

 times with two rows and additional secondary rows of tubercles 

 more or less complete. 



This genus is extinct, and is found in the oolitic cretaceous 

 rocks. 



Pedina Bakeri, Wright. PI. I. fig. 4, a-c. 



Test circular, depressed ; ambulacral areas narrow, with one row 

 of small tubercles disposed in a slightly zigzag line down the 

 centre of the areas ; interambulacral areas broad, with two rows 

 of primary tubercles raised on prominent mammillary emi- 



