254 Annals of the Carnegie Museum. 



on others obscure. It is situated in the anterior angle, above and a 

 little in front of the 'muscle spot.' The latter is large, circular, and 

 very finely reticulated. Back of the muscle spot is a region of the 

 shell which is covered with fine raised lines radiating from the side of 

 the spot. These lines frequently anastomose, making a very pretty 

 reticulate surface. The muscle spot is raised above the general surface 

 of the carapace on the lower posteror side, where these lines originate, 

 but the upper and anterior sides are level with the main part of the 

 shell. 



"The right valve overlaps the left valve considerably, especially 

 along the ventral edge, which is abruptly deflected and usually shows 

 a low short ridge right at the keel. The lower margins of the anterior 

 and posterior ends are flanged. The border is very narrow and is 

 marked by small pits, which increase in size ventrally. On one finely 

 preserved specimen the anterior flange shows eight pits, of which the 

 seventh, counted from the front, is largest, and the eighth is very small. 

 On the posterior flange of the same specimen there are ten pits, the 

 eighth from the posterior end being the largest, the ninth a little 

 smaller, and the tenth minute. The left valve is not so high in pro- 

 portion to the length as the right valve, but it is also abruptly deflected 

 ventrally. It shows neither anterior nor posterior flanges and there 

 is a small projection close to the hinge line and parallel to it. Below 

 this is a slight depression." 



Dimensions of several specimens: 



Length 10.5 mm.; height 7.5 mm. 



Length 9 mm.; height 6 mm. 



Length 9.5 mm.; height 6.25 mm. 



Length 9.5 mm.; height 7.5 mm. 



Locality. — Common on Valcour Island in certain localities. Rare 

 at Valcour and Chazy, New York. . 



2. Leperditia nana Jones. 



Leperditia canadensis Jones, 1858. Annals and Magazine Natural History, 



series 3, Vol. i, p. 244, PL 9, figs. 11-15. 

 Leperditia canadensis var. tiana Jones, 1858. Canadian Organic Remains, Decade 



III, p. 92, PI. II, figs. 6, 7, 9, 10. 

 Lepcrdilia canadensis Jones, 1884. Annals and Magazine Natural History, 



series 5, Vol. 14, p. 240. 

 Leperditia canadensis Jones, 1891. Contributions to Canadian Micro-Paleontology. 



p. 97- 



