LAMELLIBRANCHIA. 
Fig. 26. 
31 
^Jpex 
Gill of Mytilus edulis.* 
A. Part of four filaments showing ciliated interfilamentar junctions (cj). 
B. Diagram of a single filament showing the two lamellae connected at intervals 
by interlamellar junctions Cilj) and the position of the interfilamentar 
ciliated junctions (ep). 
Protobranchia. (Fig. 25, a.) 
In this order the filaments of the gills are not reflected, but 
arranged in two divergent rows, the foot being expanded and 
flattened beneath with crenulated margins and with the byssal gland 
very slightly developed. The Naculidce, and Solenomyidce are the 
only families belonging to this order. The shells of the former are 
remarkable for the numerous fine interlocking hinge-teeth, and those 
of the latter on account of the strong fringed periostracum. 
* From the ' Encyclopaedia Britannica.' Messrs. A. & C. Black, 
Case 137. 
