554 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.51. 



semielliptic in outline and its depth two-thirds of the width of the 

 anterior margin. There is a broad stippled collar on both the dorsal 

 and the ventral plate. 



The foot groove is rounded anteriorly, its sides slightly divergent 

 and somewhat cui*ved, the curvature increasing toward the posterior 

 end of the lorica. The length and width of the foot grove are nearly 

 equal and a little more than one-fourth the length of the body. The 

 posterior emargination may be evenly rounded, as in figure 1, or 

 V-shaped and slightly truncate anteriorly, as in figure 2; its depth 

 varies from two-fifths to one-half of its widtli. 



The foot is moderately stout and about one-third the length of 

 the lorica; the third joint is one-half the entire length; it has pos- 

 teriorly a sensory pit. The toes are veiy long, about one-third the 

 length of the body, and strongly asymmetric; both are slender and 

 taper gradually to veiy fine points. The right toe is straight and 

 the left toe slightly curved and bent downwards, away from the 

 right toe. The last foot joint is twisted, so that the left toe is directly 

 under the right. 



Figure 1 represents a variety from Lake Smith, near Norfolk, 

 Virginia. It differs in several respects from the normal form; the 

 anterior margin is considerably narrower and the lorica much wider. 

 The lateral spurs are broader at the base and less curved ; the posterior 

 spurs are more slender an^ somewhat longer than in the common 

 form. 



Total length, 132 ju; length of lorica 94 n, width over lateral spurs 

 75-90 n; width of anterior margin, 24-30 ju; depth of dorsal sinus, 

 8 M, of ventral sinus, 16 m; length of foot groove, 27 fx; width of 

 posterior spurs, 26-30 n; depth of posterior emargination, 10-12 /*; 

 length of foot, 28 n, of last joint, 15 ju; length of right, straight toe, 

 32 n, of left, curved toe, 27 ix; depth of body, 35 /jl. 



The distribution of this species appears to be somewhat erratic; 

 it has been recorded from Switzerland, Germany, Sweden, Norway, 

 India, Australia, and a few localities in the United States, but as a 

 rule only from restricted areas. It is of interest to note its occurrence 

 in a collection made by Mr. J. M. Jessup from lakes on Old Crow 

 River flats, on the boundary line between Alaska and Canada, 40 

 miles north of the Porcupine River, lat. 68° N., long. 141° W., or 

 well within the Arctic Circle. Where it does occur, it is, according 

 to the experience of the writer, fairly common. 



16. LEPADELLA PTERYGOIDA (Dnnlop). 



Plate 94, figs. 5-8. 

 Metopidia pterygoida Dunlop, Journ. Quekett Micr. Club, ser. 2, vol. 6, 1897, 



p. 325, pi. 17, figs. 1-3. 

 Lepadella pterygoida Harring, Bull 81 U. S. Nat. Mus., 1913, p. 64. 



The outline of the lorica is broadly oval and produced postero- 

 laterally into two roughly triangular spurs, which give the entire 



