PELECYPODA. 



Pis?. 26. 



31 



Saae 



Gill of Mytilus edulis.* 



A. Part of four filaments sliowing ciliated iuterfilamentar junctions (cj). 



B. Diagram of a single filament showing the two lamellae connected at intervals 



by interlamellar junctions Cilj) and the position of the iuterfilamentar 

 ciliated junctions (ep). 



Peotobeanchia. (Fig. 25, a.) 



In this order the filaments of the leaf -like gills are not reflected. Case 137. 

 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 Nuculidce. and Solenomyida, 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 ' Encyclopsedia Britannica.' Messrs. A. & C. Black. 



