XXVi. 
such a work as the present, will be to adopt the families (in general) 
of Fischer as used in his ‘‘ Manuel de Conchyliologie,” and to 
follow, with some minor modifications, the re-arrangement of these 
on Pelseneer’s scheme as given by Mr. B. B. Woodward, Ann. Mag. 
Nat. Hist., ser. 6, Vol xi., pp. 156-159. It appears, again, that the 
five great divisions of Pelseneer, which result in the separation of 
families so nearly related as the Arcide and Nuculide, Aviculida 
and Mytilidee, into different Orders can scarcely be justified ; and the 
explanation appears to be that our knowledge of the Pelecypoda 
has not yet arrived at a point where an ideal classification can be 
constructed. The grouping of the Families into Orders being there- 
fore somewhat in an unsatisfactory state, the Sub-orders will alone be 
used as Orders, and the general arrangement of these will be a 
combination of the two schemes which follow; the difference in 
their order being due to the fact that in one case a commencement 
has been made with the highest forms, in the other the lowest. It 
should also be borne in mind that Sub-orders and Families found in 
British waters are alone shown here. 
The two schemes consist of—(1) the Orders, Families, &c., 
as arranged by Fischer in his ‘Manuel ;” (2) Fischer’s Families 
as arranged by Mr. B. B. Woodward on Pelseneer’s scheme. 
They are printed side by side for comparison. 
PELECYPODA. 
FISCHER. WOODWARD. 
TETRABRANCHIA, SEPTIBRANCHIATA. 
Ostracea. Poromyide. 
Ostreide. Cuspidariide. 
Rumi, EULAMELLIBRANCHIATA. 
Anatinacea. 
Pectinacea. 
Anatinida (ex. Poromya) 
Limide. Lyonsiide. 
Pectinide. Pandoride. 
