1838 British Association. 



anatomy of insects. He had regarded the external tunic of the dorsal vessel of in- 

 sects as auricular. 



' On the Families of British Lamellibranchiate Mollusca,' by Prof. E. Forbes. — 

 The object of this communication is to explain a classification of the Lamellibran- 

 chiate Conchifera, intended to be adopted by the author and Mr. Hanley in their 

 forthcoming work on the British Mollusca. It is an attempt to group our native spe- 

 cies in natural families, founded upon the more important and, at the same time, con- 

 spicuous features in the organization of the animals. The characters of the mantle, 

 the siphons, and the foot, are taken as a basis, though recognized as of variable im- 

 portance in the different tribes. The general habit, and often the sculpture, of the 

 shell is usually in striking accordance with the most essential features of the animal. 

 Characters derived from the hinge and from the position of the ligament, hitherto 

 mainly depended upon by conchologists, prove to be in the majority of instances bad 

 guides for determining the natural affinities of the mollusk, and seldom of more than 

 generic value. 



The following are the separate families adopted by the authors : — 



Section A.— DYMIARIA. 



1. Pholadid^e — including Teredo, Pholas, and Gastrochena, as types of tribes ; 

 the last associated with Saxicava and Venerupis, and probably Necera, Poromya, and 

 Sphenia. Animal with a mantle closed in front, leaving a small anteal aperture for 

 the passage of the truncate or digitiform foot. Siphons united nearly to their ex- 

 tremities, their apertures cirrhated. 



2. Myad^e — including Mya, Panopcea, Lutraria, and perhaps Corbula. Mantle 

 closed, except anteally, where it is open for the passage of a thick and digitiform, but 

 not large foot. Siphons long, united to their extremities (which are slightly fim- 

 briated), enclosed in an epidermic sheath. 



3. Solen[dj3 — of which Solen is the only British genus. Mantle closed, except 

 anteally, where it is open for the passage of a very large, thick, obliquely truncate 

 foot. Margins of mantle, where free, partly fimbriated. Siphons short, united, un- 

 equal, with cirrhated margins. 



4. Solecurtid^e — Solecurtus. Mantle open anteriorly, for the large, thick, api- 

 culated foot. Siphons with an enlarged united base, divided at their extremities, and 

 having fimbriated apertures. 



5. Pandoeidje. Mantle open for a falcate foot. Siphons unequal, partly united 

 and divergent, with fimbriated apertures. Pandora, Lyonsia. 



6. TellinidjE. Mantle open and fimbriated at the margin. Foot digitiform or 

 triangular. Siphons long, separated, often nearly equal, and having plain apertures. 

 Thracia (?), Scrobicularia, Abra, and Montacuta (?), form one section of this group ; 

 Tellina and Psammobia a second and more typical division. 



7. Donacidje. Mantle open, fimbriated at the margin. Foot broadly triangular. 

 Siphons unequal, separate, and fimbriated at the edge. Donax and Mesodesma, and 

 probably also Diodonta. 



8. Venerid^;. Mantle open, fimbriated at the margin. Siphons united nearly to 

 their strongly fimbriated extremities. Foot triangular. Mactra links this group 

 with the last. Venus and its sub-genera are typical. 



9. CyprinaDjE. Mantle open, fimbriated. Siphons very short, united or nearly 

 so ; one with aperture fimbriated, the other plain. Cyprina, Astarte, Circe. 



