344 THE OCEAN WORLD. 



CHAPTEE XII. 



ACEPHALOUS MOLLUSCA continued. 







MYTILLLLZE THE MUSSEL. 



" Ecce intei' virides jactatur mytilus algas." 



Anthologia. 



WE shall now consider the nineteenth family or Mytilidae, which 

 includes Mytilus, Modiola, Lithodomus, and Dreissena. 



The well-known shell of the mussel (Fig. 157, Mytilus edulis) is 

 longitudinal, equivalve, and regular, pointed at the base, with capa- 

 city to attach itself by a byssus ; the hinge has no teeth, but a deep 

 furrow, in which the ligament is located. In the genus Mytilus the 



Fig. 157. Aiytilus edulis (Lihneeu.-). 



byssus is divided to its base. In Modiola it has a common corneous 

 centre. In Pinna the anus is furnished with a long angular base. In 

 all these genera the foot is small, its retractile muscles numerous, and 

 the byssus large. In Lithodomus the byssus is rudimentary ; the 

 muscles are retractile, equal, and two pairs only. In Unio, Cardium, 

 and Syria, the foot is large and not byssiferous. 



The animal, as described by M. Chenu, is elongate, oval, the lobes 

 of the mantle simple or fringed, divided at the edge into two leaves, 



