FROM THE CORNBRASH. 121 



The base is flat (fig. 1 b) ; the mouth opening is large (fig. 1 b d) ; the peristome is 

 deeply notched, and the surface of the test sharply everted (fig. Id); the ambulacral are 

 rather larger than the inter-ambulacral lobes ; the margins of the latter have two pointed 

 processes at the angles of the notches. 



The disc opening is large (fig. I a,e) ; but as the margin is fractured, its true diameter 

 cannot be accurately ascertained. 



Affinities and differences. — This species has so many affinities with Pseudodiadema 

 homostigma, that at one time I regarded it only as a large pentagonal variety of that 

 species ; the narrowness of the ambulacra, however (these areas being a little more than 

 half the width of the inter-ambulacra, whilst those of Pseudodiadema homostigma are 

 nearly as wide as the inter-ambulacra), added to the sudden diminution in the size of 

 the tubercles in the upper part of the areas, and the greater prominence of all the 

 bosses, induced me to separate it from Pseudodiadema homostigma. 



Locality and Stratigraphical position. — This species was collected by Mr. William Buy, 

 from the Cornbrash near Sutton, Wilts, associated with Acrosalenia hemicidaroides, 

 Wright; Acrosalenia spinosa, Agassiz; and Echinobrissus clunicularis, Llhwyd. I have 

 dedicated this species to Mr. W. H. Baily, whose crayon has so accurately delineated 

 many of the forms figured in this Monograph. 



Pseudodiadema Bakerle, Woodward. PI. VII, fig. 2 a, b, c. 



Diadema Bakerije. Woodward, Memoirs of the Geological Survey, Decade V. Notes on 

 British Fossil Diademas. 



Test sub-pentagonal, depressed ; ambulacral areas narrow, with two rows of primary 

 tubercles, about thirteen in each row ; poriferous zones narrow, pores unigeminal, near the 

 mouth trigeminal ; inter-ambulacral areas wide, with two rows of primary tubercles, larger 

 than the ambulacral, about thirteen in each row ; bosses not prominent, summits slightly 

 crenulated ; tubercles small, flat, and finely perforated ; miliary zone wide, and sparingly 

 granulated. 



Dimensions. — Height, eleven tenths of an inch ; transverse diameter, one inch and 

 four tenths of an inch. 



Description. — The specimen, unfortunately, is not in good preservation, having been 

 much weathered and bouldered (fig. 2 a, b). The ambulacral areas are narrow and 



1G 



