BRITISH FOSSILS. 



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called species just mentioned are only slight varieties, if as much, of 

 subuculus, there is, however, a white chalk Galerites, of the section 

 Discoidea, in the cabinet of Mr. Dixon, of Worthing, and figured by 

 that gentleman in his forthcoming work on the geology of Sussex, 

 which, whilst very closely allied to the species here described, presents 

 certain characters which are not present either in green-sand specimens 

 of subuculus, or in those from the white chalk itself. In form and size 

 it resembles ordinary examples of that species, and the proportion of 

 the ambulacral to the number of interambulacral plates is the same, nor 

 does the granulation of the surface materially differ. The proportions 

 of mouth and anus, and their dimensions, as compared with the entire 

 ventral surface, are so very different, and characters founded on such 

 differences appear to be so constant in this genus, that I feel bound to 

 regard it as distinct. The mouth, instead of being (as in suhuculus) 

 nearly equal in diameter to the distances between its sides and the 

 margin of the inferior surface, is scarcely half that size, and the anus, 

 instead of occupying the greater part of the space between the mouth 

 and the margin, fills less than a half of it ; consequently the appearance 

 of the base, with its perforations, is materially different, and as I can 

 find no specimens presenting intermediate characters among those of 

 the suhuculus^ either from green sand or chalk, I feel bound to consider 

 this a distinct species, and have named it Galerites {Discoidea) Dixoni. 



In the preceding account of Galerites suhuculus^ and in my notes on 

 Galerites suhcylindrica (Dec. i., pi. viii.) I have considered the Galerites 

 rotula of Alexander Brongniart (Geognosie des Terrains de Paris, pi. 

 9, f. 13, A. B. C.) as identical with the former species, and his figure as 

 a representation of a large specimen of it. I am induced to do so on 

 account of the evident manner in which the subcarination of the halves 

 of the interambulacral spaces are indicated in his figure (13 A.), whilst 

 the inferior surface is represented as thickly covered with nearly equal 

 tubercles. Unfortunately no figure of the anus is given, to enable us to 

 decide with more certainty. On one of the figures an appearance as if 

 of a supramarginal anus is indicated, and this no doubt has led M. 

 Charles Des Moulins to regard it as a Pyrina, and to name it Pyrina 

 rotula. If his view of its characters be correct, it has certainly nothing 

 to do with the section Discoidea. Agassiz has, however, considered 

 Brongniart's figure as the type of his Discoidea rotula — a very different 

 species, and which, since our note of Galerites cylindricus was put in 

 type, I am still more inclined to identify with the Discoidea there de- 

 scribed, from the junction beds of the chalk and green sand, and of 

 which Mr. Morris has afforded me opportunities of seeing a number 

 of specimens, of dififerent ages, from Charldon, in Dorsetshire. An 

 examination of them, and of their ca«ts, confirms me in my opinion of the 



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