DESCRIPTION OF GENERA AND SPECIES. 
Orprr—PROSOBRANCHIATA, Milne Edwards, 1848. 
Note.—As already observed in the General Introduction there are certain genera of Gasteropods 
whose family position is yet doubtful, and which have been variously located by different authors. 
Purpurina and Brachytrema are noteworthy instances of such uncertainty. It is proposed to consider 
these in the first instance without attempting to refer either genus to any particular family. 
Genus—Purpugina, D’Orbigny, 1850, Prod. i, p. 278. 
Shell deeply and narrowly perforate, oval-elongate, tumid, thick ; whorls rounded, 
rendered angular posteriorly by the sutwral canaliculation; body-whorl large, 
ornamented with longitudinal ribs crossed by spiral strie; aperture oval, sub- 
canaliculate in front ; columella arched ; lip simple.—Fiscuer. 
Bibliography, §c.—Defined by Deslongchamps, 1860 (‘ Bull. Soc. Linn. Norm.,’ 
vol. v, p. 136). 
The history of Purpurina is rather singular. D’Orbigny gives a short 
diagnosis in the ‘ Prodrome,’ and names several species from the Bajocian, 
Bathonian, Callovian, and Oxfordian; all of which perhaps belong to the genera 
Brachytrema and Purpuroidea of Lycett. In the ‘ Terrains Jurassiques,’ as is well 
pointed out by Deslongchamps, numerous figures of Purpwrina are given in the 
atlas, most of which belong to the genus Hucyclus (Amberleya). In the text 
D’Orbigny says nothing about the genus Purpwrina, nor is there a word of 
description of any of the species figured. Fortunately there is just one figure of a 
most characteristic form, P. bellona, D’Orb. (‘ Ter. Jur.,’ pl. 331, figs. 1 and 3), from 
the Inferior Oolite of Bayeux, and this has been accepted both by Piette (‘ Bull. 
Soe. Géol. de la France,’ 2nd series, vol. xviii, p. 587) and by Deslongchamps for 
the type of a genus which, as defined by them, has relations on one side with 
Turbo and on the other with Cerithiwm and Purpura. ‘These shells,” says 
Deslongchamps (vol. cit., p. 176; p. 24 of the separate ‘ Memoir on the Fossils of 
Montreuil-Bellay), “are characterised by a thick test, a small groove more or less 
pronounced in front of the mouth, especially in early life, by an umbilical slit of 
