8 BRITISH JURASSIC GASTEROPODA. 
this method as applied to existing creatures, we must fall back upon the shell as 
the basis of classification for our fossils, and accept such aid from zoology as is 
consistent with the material at our disposal. 
It would seem as though the interest in the study of the Mollusca had been 
reviving lately. This may be inferred from the fact of the publication of three 
useful and important manuals since the beginning of 1880. I allude (1) to the 
fourth edition of Woodward’s ‘ Manual,’ with appendix by Prof. Ralph Tate ; (2) 
to the work on ‘Structural and Systematic Conchology,’ by George W. Tryon, 
junr., published at Philadelphia; and (8) to the ‘Manuel de Conchyliologie,’ by 
Dr. Paul Fischer, of which the portion completing the Gasteropoda appeared in 
February, 1886. This work is being published in Paris. These authors, as also 
Stoliczka in the ‘ Palwontologica Indica,’ bear testimony to the invaluable 
character of the original Manual by 8. P. Woodward, which is indeed, both as 
regards text and illustrations, a work of the very highest character, published at a 
price which places it within the reach of all. 
With some important exceptions I hope to follow in the main the classification 
of the ‘ Manual of the Mollusca.’ The most important exceptions are (1) in the 
position assigned to the Aporrhaide and Cerithiide ; (2) in adopting the family 
of the Pseudomelaniide, to include the quondam Chemnitzias and possibly some of 
the Phasianellas of the Jurassic Rocks. It should be noted that 8. P. Woodward 
always regarded the application of the term Chemnitzia to the great Melania-like 
shells of the Jurassic Rocks as provisional, and many paleontologists besides that 
author have felt dissatisfied with the arrangement. Still, I should scarcely have 
ventured on such an innovation without the sanction of Dr. Paul Fischer, whose 
high authority I must quote in justification. I have long wished to do this, and 
now in such good company have no further hesitation. 
There are certain genera, moreover, in the Jurassic Rocks whose position seems 
very doubtful. Most of those to which I allude are more or less characteristic of 
beds of thatage. A few may be mentioned here, though each genus will of course be 
fully dealt with in the descriptive part of the text. Any observations now made 
must be regarded as preliminary and incomplete. 
The first of these is Purpurina, a genus founded but abandoned by d’Orbigny, 
who makes no mention of it in the text of the ‘ Terrains Jurassiques.’ From the name 
given we may judge that the author would have placed his genus in the same 
family as Purpura. The genus Purpurina were practically reconstituted by Piette 
and Deslongchamps, who regarded it as having relations on the one side with Turbo, 
and on the other with Cerithium and Purpura. If these views be correct its family 
relations are by no means clear, and this circumstance may account for the 
contradictory position assigned to it by the various authorities. Thus Tryon 
places Purpurina, with a query, under the sub-family Purpurine, and also under 
