1869.] 153 [Perkins. 



Sphserium partumeium Prime, Am. Corbie, p. 45, fig. 42. 

 Cyclas partumeia Say, Am. Conch., p. 112, 1822; Gould, Invert, Mass., 

 p. 73, fig. 54; De Kay, Moll. N. Y., p. 223, pi. xxv, fig. 262. 



Rare and small. 



Sphserium solidulum Prime, Am. Corbie., p. 36, fig. 27. Cy- 

 clas solidula Prime, Proc. Bost. Soc. Nat. Hist., Vol. iv, p. 158, 1851. 



Animal white; mantle open, edged with an orange cord; gills 

 rather narrow; foot long, tongue-shaped; palpi long and narrow, 

 rounded at the tips; siphons distinct, simple at the ends, not long, 

 broad, ventral nearly twice as large as the dorsal, orange or reddish 

 yellow, or rarely white; shell filled with young in May, usually con- 

 taining ten of various sizes; some are contained in the gills and some 

 in the mantle, the largest being four mill, long, three broad and two 

 high. 



Sphasrium securis Prime, Am. Corbie, p. 49, fig. 47. Cyclas 

 securis et cardissa Prime, Proc. Bost. Soc. Nat. Hist., Vol. iv, p. 160, 

 1851. 



Not uncommon in some ponds. The foot is very long and narrow, 

 and the animal, like the Pisidiums, crawls very rapidly by extending 

 it fully and, holding by the end, drawing the shell near to it. In 

 this way they crawl up the sides of a glass vase with ease, though a 

 slight jar causes them to fall. 



Pisidium Pfeiffer, 1821. 



Pisidium sequilaterale Prime, Am. Corbie, p. 63, figs. 65, 66; 

 do. Bost. Journ. Nat. Hist., Vol. vi, p. 366, pi. xii, figs. 23-25. 



Lives in ponds but is not common. Animal flesh color; foot very 

 long, strap-shaped, rounded at the tip; siph ons v ery short, tapering, 

 simple at the ends. 



Pisidium abditum Haldeman, Proc. Acad. Nat. Sc. Phil., Vol. i, 

 p. 53, 1841; Prime, Am. Corbie, p. 68, fig. 72; De Kay, Moll. N. Y., 

 p. 226. Pisidium obscurum Prime, Bost. Journ. Nat. Hist., Vol. iv, 

 p. 161. Pisidium minus Stimpson, Shells of N. E., p. 16. 



Not common. Lives in quiet ponds. 



Pisidium compressum Prime, Proc. Bost. Soc. Nat. Hist., 

 Vol. iv. p. 164; do. Am. Corbie, p. 65, fig. 68. 



Not common. Lives in ponds and ditches. 



Pisidium variabile Prime, Proc. Bost. Soc. Nat. Hist., Vol. iv, 

 p. 163; do. Am. Corbie, p. 66, fig. 69. 



Not very rare. 



