452 Annals of the Carnegie Museum. 



more rounded, and the appearance of the surface is somewhat different. 

 It appears that the two Pisidia (Nos. 30 and 31) are conspecific, 

 although intermediate and connecting forms have not been seen. 

 If this view be correct, P. fraudidentiim should be regarded as typical, 

 being widely distributed, even though such procedure would be 

 contrary to the formal rule of priority. . 



Ha bitat. — Michigan. 



Fossil. — Michigan, Ohio (?). 



32. Pisidium latchfordi sp. nov. 



Mussel small, ineciuipartite, oblique, nearly oval in lateral aspect, 

 well inflated; beaks somewhat posterior, rather large, prominent, 

 rounded; superior margin curved, supero-anterior slope slightly 

 marked, short, anterior end rounded, well below the longitudinal 

 axis; posterior part short, subtruncate, or rounded; surface slightly 

 glossy, with very fine and slight microscopic striae, colorless to whitish, 

 shell translucent to opaque; hinge rather long, curved-angular, stout, 

 plate rather broad, short; right cradinal tooth well curved, not much 

 projecting, its posterior end not or but little thicker; between it and 

 the somewhat projecting lower edge of the plate there is an elongate- 

 triangular excavation for the left anterior, well-defined all around; 

 left anterior set rather well up on the plate, small, posterior oblique, 

 curved; laminae rather massive, with their surfaces rugose, the 

 anterior and posterior at right angles to each other; cusps of the left 

 ones pointed, with the proximal and distal slopes steep and almost 

 equal, those of the right inner less pointed, outer anterior about one- 

 third the length of the inner, posterior short and small; ligament 

 short, resilium stout. 



Measurements. — Long. 2.6; alt. 2.4; diam. 1.9 mm. (100 : 93 : 73). 



Habitat. — Ontario, apparently rare. Collected in 1913 by High 

 Justice F. R. Latchford, in whose honor the species is named. It 

 occurs in Scott Graham Creek, Graham Bay Creek, and Hare's Spring, 

 all in Carleton County, Ontario. Specimens are in the collection of 

 Justice Latchford and in the Carnegie Museum, Nos. 7,439 and 7,475. 

 Only a rather small number of specimens are at hand, but markedly 

 uniform, and different from all other described species. Their shape, 

 the formation of the hinge, and the stout, short ligament and resilium 

 place them in a group with P. ccquilaterale, fraudidenticm, etc. "^ 



