358 A Monograph of the Species of Pisidium. 
beaks ; hinge margin much rounded ; cardinal teeth united ; 
lateral teeth elongated. 
Dimensions. Long. 0.095 ; lat. 0.075 ; diam. 0.08 inches. 
GEOGRAPHICAL DISTRIBUTION. Lake Superior, (Agassiz.) 
Osservations. This minute species bears some resem- 
blance to the P. ventricosum, but it is less inflated, more equi- 
lateral; the margins are more rounded, and the beaks are 
larger and more prominent. 
8. Pisrptum mENELLUM Gould. 
Cabinet of the B. S. N. H. 
Pk XI. Fig. 21, 99, 93. 
Pisidium tenellum Goutp. Agassiz’s Lake Md 210. 
Pisidium rubellum Nonis. Bost. S. N. H. Proc. iv. 163. 
Description. Shell small, fragile, subglobose ; margins 
well rounded ; beaks full, well rounded, and approximate, not 
tumid ; striations not heavy ; ; color light yellow ; pou shel 
more inilatód and shorter than adult; hinge margin gently 
curved ; teeth all very rudimentary. 
DisishHonk: Long. 0.07; lat. 0.14; diam. 0.10 inches. 
GEOGRAPHICAL DISTRIBUTION. Lake Superior, (Agassiz.) 
OBSERVATIONS. Compared to the P. minus, this species is 
more full, the outline is more circular and less elongated ; 
the beaks are not so tumid, and the whole shell is smaller. 
In outline it is somewhat similar to the P. abditum, but the 
teeth are totally diferent, as also the coloring. 
