992. TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
with the horizontal septum, which continues forward the 
fusion of the mantle edge between the two siphons, and 
consequently they form the floor of the ventral supra- 
branchial chamber which is a continuation forward of the 
cavity of the dorsal siphon. This ventral suprabranchial 
chamber is continuous with a series of cavities between 
the two lamelle of the right and left inner branchie. 
The reflected lamellae of the outer branchiz, on the other 
hand, are filamentar in structure through all their width, 
and extend dorsally beyond the ctenidial base to be 
inserted into the body-wall in the angle formed by the 
latter and the mantle lobes. This dorsal extension of the 
reflected lamelle of the outer branchie is common to a 
number of Eulamellibranchs, of which Cardiwm forms 
the type, and is the “‘appendice”’ of Pelseneer, which is 
regarded by him as the beginning of a third lamella of the 
outer branchia.* 
The branchie of Cardiwm are of the “fluted or com- 
pound type,” that is, each is thrown into a number of deep 
furrows and ridges, the direction of which is perpendicular 
to the base of the ctenidium. ‘Two such ridges, with a 
furrow between, are represented in fig. 26— where the 
branchia is cut in a plane at right angles to the filaments. 
Each ridge consists of a group of from 20 to 30 filaments. 
One or two filaments may occupy the summit of the ridge, 
the bottom of the furrow is constituted by two filaments 
which have opened out and fused by their edges forming a 
membranous plate. In each branchia these ridges and 
furrows are symmetrically opposed to each other, ridge 
against ridge, and furrow against furrow. The supra- 
branchial cavity extends into the interior of each ridge. 
Morphologically the branchia consists only of this 
* Bull. Sci. de la France et de la Belgique. Ser. III., t. XX., pp. 27—52 
1889, 
