536 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 51. 



16. Foot groove very wide 1 . apsida, new species 



Foot groove very narrow 9. dadyliseta (Stenroos). 



17. With a dorsal spine 19. cristata (Rousselet). 



Without dorsal spine 18. 



18. With dorsal sinus 18. rhomboides (Gosse). 



Without dorsal sinus 19. 



19. Lorica ovate 17. imbricata Harring. 



Lorica rhomboid or subcircular 20. 



20. Keel of moderate height, anterior dorsal margin slightly concave. 



20. rhomboidula (Bryce). 



Keel very high, anterior dorsal margin with a shallow notch between two convex 



lobes 21 . triptera Ehrenberg. 



1. LEPADELLA APSIDA, new species. 



Plate 89, figs. 1-3. 



The body of this small species is nearly circular in outline; the 

 dorsal plate is moderately convex and its edges project slightly 

 below the general level of the nearly flat ventral plate. The depth 

 of the body is less than half the width of the lorica at its widest 

 point. 



The opening for the head is circular; there is consequently no 

 dorsal sinus, but, on the contrary, the anterior dorsal margin is 

 convex. In order to permit the free movement of the head the 

 ventral plate projects downwards around the anterior sinus. No 

 stippled collar is present, but there is a beadlike line around the 

 posterior half of the ventral sinus and shghtly removed from the 

 edge; it does not foUow a coiu-se parallel to the edge of the ventral 

 sinus, but, as shown in the ventral view, forms roughly five sides of a 

 regular octagon. 



The foot groove is U-shaped and rounded anteriorly; its length is 

 about one-third that of the lorica and the width slightly gi*eater. 

 There are no posterior spines or other projections at the junction of 

 the lateral edges of the foot groove and the posterior margin of the 

 lorica. 



Tlie foot is fairly stout and short, the joints increasing slightly in 

 length from the basal to the posterior. The toes are very short, 

 less than one-sixth the length of the lorica, and taper regularly to 

 acute points. A sensory pit on the terminal joint has not been 

 found; this may be partly or entirely accounted for by the diffi- 

 culties of observation. 



Total length, 84 ^u; length of lorica, 70 /x, width 60 n; length of 

 head opening 20 ju, width 24 /x; length of foot groove 22 fi, width 

 24 ^; length of toes, 12 )u; depth of body, 24 ix. 



Type.— Cat. No. 16826, U.S.N.M., is from East Swamp, South 

 Bass Island, Lake Erie; this species has also been found in collec- 

 tions from ponds in Audubon Park, New Orleans, Louisiana. The 

 material was in both cases collected by Dr. E. A. Bu-ge, of the Uni- 

 versity of Wisconsin. 



