Fig. 79. 



P. ventricosum. 



72 AMERICAN CORBICULAD^E. 



13. Pisidilim veiitricosum, PRIME. Shell small, rounded- 

 oval, globose, ventricose, somewhat oblique, slightly in 

 equilateral, anterior side produced, posterior subtruncate ; 

 beaks small, protuberant, distant, situated towards the 

 posterior side ; surface smooth, yellow ; hinge-margin 

 curved ; cardinal teeth separate ; lateral teeth short. 

 Long. 0.11 ; Lat. 0.095 ; Diam. 0.085 inches. 



Hab. North America, in the State of Massachusetts. 



Cabinets of the Boston Society, Smithsonian Institution, 

 Lewis, Jay, Prime, and others.) 



Pisidium ventricosum, PRIME, Bost. Proc. IV, L C 51, 68. 

 Musculium ventricosum, ADAMS, Rec. Gen. II, 1858, 452. 

 Pisum ventricosum, ADAMS, loc. sub. cit. II, 1858, 660. 



This small, globose species is not likely to be confounded with 

 any other but P. rotundatum, than which, however, it is more 

 oblique, the margins are more abrupt, and the beaks more terminal 

 and very much smaller. It is very nearly allied to P. oUusale, 

 of Europe. 



Fig. 80. 



P. ventricosum. 



Fig. 81. 



14. Pisidilim rotini datum, PRIME. Shell small, rounded- 

 oval, globose, ventricose, inflated, subequilateral ; anterior 

 and basal margins rounded, posterior margin somewhat 

 abrupt; anterior side a little longer : beaks nearly central, 

 very large, prominent, rounded ; surface glossy, yellow, 

 somewhat darker in the region of the beaks ; hinge-margin 

 curved ; teeth small. 



Long. 0.09; Lat. 0.07; Diam. 0.08 inches. 



P. rotundatum. 



Hab. North America, in the region of Lake Superior. (Cabinets of 

 Agassiz and Prime.) 



Pisidium rotundatum, PRIME, Bost. Proc. IV, 1851, 164. 

 Musculium rotundatum, ADAMS, Rec. Gen. II, 1858,452. 

 Pisum rotundatum, ADAMS, loc. sub. cit. II, 1858, 660. 



