400 THE CHICAGO ACADEMY OF SCIENCES. 



imens. Also in the formation of the cardinal teeth there is 

 some variation, as the one in the right valve may be indented 

 in its middle at the angle, and so there are apparently two 

 teeth." (Sterki.) 



154. Pisidium splendidulum Sterki, pi. xxxi, fig. 23. 



Pisidium splendidulum STERKI, The Nautilus, Vol. XI, p. 113, 1898. 



Shell: "Mussel small, well inflated, rather ovoid in out- 

 line, scutum and scutellum rather well marked, the former 

 often prominent; beaks slightly posterior, somewhat promi- 

 nent, moderately large, rounded; color pale to deep horn, sur- 

 face polished, with very fine, somewhat irregular striae; shell 

 thin, transparent; hinge rather fine but well formed, plate nar- 

 row; cardinal teeth longitudinal, lamellar, the right one rather 

 long, slightly curved, most so at both ends, more or less thick- 

 ened at the posterior end, and often with a groove; the two in 

 the (left) valve nearly equal, parallel, little curved, the superior 

 is anterior for about one-third of its length; lateral teeth com- 

 paratively strong, all projecting into the interior of the mus- 

 sel, pointed; ligament rather long." (Sterki.) 



Length, 2.80; height, 2.40; breadth, 1.70 mill. (Sterki.) 



Animal: Unknown. 



Distribution: Caribou, Saco and Old Orchard, Maine; 

 Grand Rapids, Mich.; Washington, D. C.; Virginia, near Wash- 

 ington (Sterki); Lilycash Creek, near Desplaines River, Illi- 

 nois (Handwerk). 



Habitat: In creeks, brooks and rivers, buried in soft mud. 



Remarks: "Our species cannot be mistaken for any other 

 Pisidium. In shape it has some resemblance with P. abditum 

 undpolitum; but its small size, the color and transparency of 

 the shell, and the shape of the cardinal teeth, will readily distin- 

 guish it. In size, color and transparency of the shell, and the 

 polished surface, it resembles P. ventricosum and vesiculare ; but 

 both the latter are much more inflated, their beaks are quite 

 posterior and larger. It is, however, rather variable in size and 

 coloration, and in the striation of the surface." (Sterki.) 



This new species is very common wherever it has been 

 found in the Eastern states, and it may be looked for in con- 

 siderable quantities in our Western states. 



155. Pisidium fallax Sterki, pi. xxxi, fig. 16. 



Pisidium fallax STERKI, The Nautilus, Vol. X, p. 20, 1896. 

 Pisidium fallax var. septentrionale STERKI, The Nautilus, Vol. XII, 

 No. 7, p. 78, 1898. (non Prime.) 



