60 CONCHOLOGY. 



P. glycimeris. P. pectiniformis. 



P. undulatus. P. nummarius. 



P. scriptus. P. radiaus. 



P. stellatus. P. vitreus. 



P. violacescens. P. inscriptus. 



P. aggregatus. P. cinerosus. 



4. Genus JVucula. 

 minimal. Body subtriquetral ; mantle open in its inferior half 

 only, with whole edges, denticulated throughout the extent of the 

 back, without posterior prolongation ; foot very large, thin at the 

 root, enlarged into a wide oval disk, the edges of which are fur- 

 nished with tentacular digitations ; anterior buccal appendages, 

 pretty long, pointed, stiff, and applied one against the other like 

 jaws ; the posterior ones also stiff and vertical. 



Shell. More or less thick, subtriquetral, equivalved, inequilat 

 eral, with summits contiguous and inclined anteriorly; hinge 

 similar, formed by a numerous series of very sharp teeth, pecti- 

 nated and arranged in a line interrupted under the summit ; liga- 

 ment internal, short, inserted in a little oblique pit in each valve ; 

 two muscular impressions. Inhabits the British seas. Forty living 

 species. Four fossil. 



Nucula lanceolata. Nucula rostrata. 



jN, pella. N. Nicobarica. 



N. obliqua. N. Margaritacea. 



N. elongata. N. costellata. 



N. tellinoides. N. gibbosa. 



N. crenifera. N. eburnea. 



N. arctica. N. polita. 



N. curvirostra. N. nasuta. 



N. glacialis. N. fabula. 



N. fluviatilis. N. Elenensis. 



N. minuta. N. cuneata. 



N. para. N. striata. 



N. Mauritiania. N. rugulosa. 



N. limatula. N. nitida. 



N. laevis. N. tenuis. 



