DESCRIPTION OF GENERA AND SPECIES. 



Order— 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 mstance without attempting to refer either genus to any particular family. 



-Purpurina, D'Orbigny, 1850, Prod, i, p. 278. 



Shell deeply and narrowly perforate, oval-elongate, tumid, thick ; whorls rounded, 

 rendered angular posteriorly by the sutural canaliculation ; body-whorl large, 

 ornamented with longitudinal ribs crossed by spiral striae; aperture oval, sub- 

 canaliculate in front; columella arched; lip simple. — Fischer. 



Bibliography, Sfc. — 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 Purpurina are given in the 

 atlas, most of which belong to the genus Eucyclus (Amberleya). In the text 

 D'Orbigny says nothing about the genus Purpurina, 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.,' pi. 331, figs. 1 and 3), from 

 the Inferior Oolite of Bayeux, and this has been accepted both by Piette (' Bull. 

 Soc. G-eol. 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 Cerithium 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 



