456 Annals of the Carnegie Museum. 



53. Pisidium friersoni Sterki. 



Pisidium friersoni Sterki, Nautilus, XX, 1906, p. 20. 



Habitat. — Louisiana, Texas, Arkansas, Colorado. 



54. Pisidium atlanticum Sterki. 



Pisidium atlanticum Sterki, Nautilus, XVIII, 1905, p. 128. 

 Habitat. — Georgia, Florida to Texas, Arkansas. 



55. Pisidium atlanticum dispar Sterki. 

 Pisidium dispar Sterki, Nautilus, XXV, 1911, p. 2. 



Less oblique, beaks narrower. 

 Habitat. — -Alabama. 



56. Pisidium atlanticum albidum Sterki. 



Pisidium albidum Sterki, Z. c , p. 2. 



Less oblique; surface dull, with coarser, sharper striae. 

 Habitat. — Alabama. 



57. Pisidium trapezoideum Sterki. 



Pisidium trapezoideum Sterki, Nautilus, IX, 1896, p. 124. 



Habitat. — Eastern Pennsylvania to Virginia, apparently near the 

 coast. 



58. Pisidium trapezoideum protensum var. nov. 



Mussel more oblique, larger, anterior part much longer. Specimens 

 are contained in the collection of Mr. W. G. Mazyck, No. 662, and in 

 the Carnegie Museum, No. 7387. 



Habitat. — Columbia, Pennsylvania. 



59. Pisidium neglectum Sterki. 



Pisidium neglectum, Sterki, Nautilus, XX, 1906, p. 87. 



Near the palearctic P. pusillum (Gmclin) Jenyns, and possibly 

 conspecific. 



Habitat. — East of the Rocky Mountains, apparently rare in the 

 South. 



Fossil. — Ohio. (Probably overlooked elsewhere.) 



60. Pisidium neglectum corpulentum var. nov. 



More inflated ; beaks larger and more prominent; upper margin 

 more curved. While markedly different from P. neglectum, and 

 apparently distinct, there seem to be intermediate forms; but the 

 specimens from a given locality are generally of one form only. 



