PHOLAS. 101 



that the Tunicata were shell-less Pholades. Schumacher 

 ranged Pholas with the pedunculated Cirripeds, and 

 Teredo in another division of his medley collection 

 of Monothalami. In Blanchard's system the present 

 family is regarded as closely allied to the Myida*. The 

 number and position of the dorsal shields are useful 

 characters to distinguish sections of genera, but they do 

 not appear to be of any greater value. Ever since the 

 groups called families were instituted in classifying the 

 animal kingdom, conchologists have been busy in framing 

 synonyms for the one of which we now treat. These 

 synonyms, with the exception of two (Adesmacea, De 

 Blainville, and Cladopoda, Gray), were compounded out 

 of the generic name Pholas ; and the ingenuity of the 

 systematists may well excite our admiration, or some 

 other feeling of perhaps not a laudatory kind, when we 

 find no less than fourteen of such compositions. 



Genus I. PHOLAS*, Lister. PL IV. f. 1. 



BODY oblong or oval, usually incapable of being altogether 

 contained within the shell : tubes united except at their ex- 

 tremities, and enveloped in a membranous retractile sheath, 

 as in My a ; both orifices cirrous : gills nearly equal : palps 

 large and broad : foot truncated, but expansible to a certain 

 extent. 



SHELL shaped like the body, nearly opaque and lustreless, 

 more or less covered with rows of prickles : beaks concealed 

 by a fold of the hinge-plate in each valve : apophyses long and 

 partly concealed within the hinge : paJlial scar narrow and 

 deeply sinuated : muscular scars widely separated ; anterior 

 elongated, posterior short : dorsal shields usually present, and 

 varying in number, size, and position; when absent, their 

 place is supplied by a tough integument of the mantle. 



The present genus is not so ancient as has been gene- 



* Lurking in dens. 



