556 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 51. 



foot groove, 22 fx, width, 12 /i; width of posterior margin of lorica, 

 12 fi; length of foot, 21 fj., of last joint, 9 n; length of toes, 20 /x; 

 depth of body, 23 /x. 



This description is from a single specimen, found in moss from the 

 gravel pit at Hyattsviile, Maryland. It differs in a number of points 

 from Dunlop's original description and Dixon-Nuttall's figure; Dmi- 

 lop's animal is considerably narrower anteriorly, but this may possi- 

 bly be due to his having studied an extended specimen; the figure 

 shows a median ridge on the dorsal plate, which is certainly not pres- 

 ent in the Hyattsviile specimen; the mtermediate pair of ridges are 

 shown as similar in form to the other two pairs, while in my specimen 

 there are two distinct keels projecting above the general level of the 

 dorsal plate. However, the similarity is so great that the existence 

 of two species seems improbable, and we may perhaps ascribe some 

 of the differences to difficulties of observation, others to the known 

 variability of the membei-s of this genus. 



Lepadella pterygoida is evidently extremely rare; Dunlop found 

 only two specimens. With the single specimen here described the 

 records of its appearances seem to be exhausted. 



17. LEPADELLA IMBRICATA Hairing. 



Plate 95, figs. 9-11. 



Lepadella imbricata Harking, Proc. U. S. Nat. Mus., vol. 47, 1914, p. 549, pi. 16, 

 figs. 3-5. 



The lorica is ovate in outUne and very slightly constricted at the 

 anterior margin. The dorsal plate is tectiform with a shallow groove 

 on each side, equidistant from the edge of the lorica and an incon- 

 spicuous median ridge ; its edges project very shghtly below the nearly 

 flat ventral plate. The cross section of the body is obscurely tri- 

 radiate; in this respect L. imhricata is the least specialized member 

 of the Metopidia group. The doi-so- ventral depth of the body is 

 nearly one-half the length of the lorica. 



The width of the anterior margin is a httle less than one-third the 

 length of the lorica. No dorsal sinus is present, the frontal edge of 

 the dorsal plate being nearly straight. The ventral sinus is broadly 

 V-shaped and pointed posteriorly; its depth is two-thirds of the 

 width of the anterior margin. Neither a stippled collar nor the bead- 

 like thickening of the anterior margin occasionally taking its place is 

 present in this species. 



The foot groove is U-shaped and very narrow, rounded anteriorly 

 and with parallel sides; its length is a little less than one-third the 

 length of the lorica and the width somewhat more than half the 

 length. The lorica is rounded posteriorly, without any emargination. 



The foot is nearly two-fifths of the length of the body and quite 

 slender; the terminal joint is more than half the entire length. No 



