ANODONTA CYGNEA & BUCCINUM UNDATUM. 115 



PLATE XVI. 

 SPECIMEN 1. 

 Ventral view of the animal of the Fresh-water 



Mussel, 

 Anodonta cygnea, Linnaeus. 



Showing the mantle, gills, mouth, labial palps, foot, and 



anus. 



This bivalve is a typical illustration of the Class 

 LAMELLIBRANCHIATA, and also of the Conchological 

 Division, Bivalve Shells. The MANTLE (as seen in 

 the illustration) is the portion immediately below the 

 words FOOT, GILLS, and above PALPS, MANTLE. It is 

 developed on both sides of the animal, and is divided into 

 a right lobe and a left lobe ; the MANTLE indicator 

 terminates in front of the right lobe. The mantle secretes 

 over the whole of its outer surface, a deposit, consisting of 

 carbonate of lime and an organic matrix known as 

 conchyolin. In addition, there is a thick, calcareous 

 layer, and on the exterior of each valve there is a horny 

 cuticle, or periostracum. See plate XIII., fig. 8. 



The LABIAL PALPS may be regarded as expansions of 

 the margins of the mouth. The surface of each is thickly 

 covered with cilia, which create currents of water carrying 

 food to the mouth. As will be seen in the illustration, 

 they are lobed, the median groove being very distinct. 



Jaws and tooth-ribbon, or radula, are absent. The 

 mouth is connected to the stomach by a short oesophagus. 

 The remainder of the alimentary canal is of considerable 

 length, and greatly convoluted, terminating at the ANUS. 



The FOOT can be used by the animal to assist its 

 movements along the bottom of the pond, or river, and 

 enables it to bury itself in the mud. It is very muscular 

 and powerful. Within it is contained some of the viscera. 

 It can be protracted at will by the creature by turgescence 

 with blood. Retraction is accomplished by retractor 

 muscles. 

 SPECIMEN 2. 



The animal and portion of shell of the 

 Common Whelk. 



Bucdnum Undatum, Linnaeus. 



Showing the proboscis enclosing toothed band, tentacles, 

 eyes, syphon, mantle, foot, gill, and reproductory organ. 



