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. Try on, 

 junr., published at Philadelphia; and (3) 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 ' Paleeontologica Indica,' bear testimony to the invaluable 

 character of the original Manual by S. 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 Aporrhaidse and Cerithiidaa ; (2) in adopting the family 

 of the Pseudomelaniidse, to include the quondam Ohemnitzias and possibly some of 

 the Phasianellas of the Jurassic Rocks. It should be noted that S. P. Woodward 

 always regarded the application of the term Chemnitzia to the great Melania-like 

 shells of the Jurassic Rocks as provisional, and many palaeontologists 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 that age. 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 Try on 

 places Purpurina, with a query, under the sub-family Purpurinae, and also under 



