96 The Ottawa Naturalist. [November 



jecting, 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 Hon. 

 Justice Latchford, in whose honour 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. aequilaterale, fraudulentum, etc. 



["Hare's Spring" is on the Hare farm, Nepean, near the Watson 

 line, about five hundred yards south of the Richmond Road.] 



80. PlSIDIUM SUBROTUNDUM CANADENSE var. nOV. 



Mussel larger. Long. 5.5; alt. 4.6; diam. 3.4 mm. More oblique; 

 beaks more posterior; upper margin markedly straight, slightly alate 

 in front of the beaks and bounded by an agle. In shape they some- 

 what resemble P. ovum from Montana, but are less inflated, and the 

 hinges are different. Some specimens in the same lot have the beaks 

 narrower, and are more markedly different from P. subrotundum. 



Habitat. Hare's Spring, Carleton County, Ontario, collected 

 in considerable numbers by Justice Latchford. Represented in his 

 collection, and in the Carnegie Museum, No. 7,437. May be distinct. 



84. Pisidium vexum sp. nov. 



Mussel small, slightly inequipartite and oblique, rather well 

 inflated; beaks slightly posterior, rather broad, more or less flatteneu 

 on top, moderately prominent, descending abruptly towards the 

 posterior part; superior margin nearly straight, bounded by angles, 

 posterior margin subtruncate or rounded, passing into the moderately 

 curved inferior without an angle, anterior end rather broadly rounded, 

 supero-anterior slope marked, nearly straight; surface dullish to some- 

 what shining, with very fine and slight subregular stria?. Shell thin, 

 translucent to transparent, colorless; hinge rather slight, but well 

 formed, moderately long, plate rather narrow; cardinal teeth rather 

 long, the right curved to nearly straight in its middle, its posterior end 



