558 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.51. 



The foot is approximately one-third the length of the lorica and 

 fairly stout; the third joint is a little longer than both anterior joints 

 and has a dorsal sensory pit. The toes are short, less than one-fourth 

 the length of the body; they are slightly decurved and taper rather 

 rapidly to slender points. 



Total length, 156 m; length of lorica, 120 n, width, 80 ju; width of 

 anterior margin, 29 n; depth of dorsal sinus, 11 /x, of ventral sinus, 

 20 fx; length of foot groove, 37 n, width, 19 ju; length of foot, 35 ju, 

 of last joint, 19 n; length of toes, 26 n; depth of body in median 

 plane, 36 n, to edges of lorica, 44 /x. 



This species is widely, but apparently rather irregularly distributed; 

 it usually occurs in small numbers. 



19. LEPADELLA CRISTATA (Rousselet). 



Plate 96, figs. 5-12. 



Colurus cristatus Rousselet, Journ. Royal Micr. Soc, 1893, p. 446, pi. 7, fig. 2. 

 Metopidia cristata Voronkov, Trudy Hidrobiol. Stants. Glubokom Oz., vol. 2, 



1907, p. 112, pi. 7, figs. 39-42. 

 Metopidia nma-onata Daday, Math. Term. Ert., vol. 26, 1908, p. 30; not Lepa- 



della mucronata Schmarda, 1859. 

 Metopidia semicarinata Lucks, Ber. Westpreuss. Bot.-Zool. Ver., vol. 31, 1909, 

 p. 141. — DiEFFENBACH, S usswasserf auna Deutschlands, pt. 14, 1912, p. 189, 

 text fig. — Lucks, Rotatorienfauna Westpreussens, 1912, p. 124, text fig. 

 Metopidia semicarinata tripteris Lucks, Ber. Westpreuss. Bot.-Zool. Ver., vol. 31, 

 1909, p. 141. — DiEFFENBACH, Susswasserfauna Deutschlands, pt. 14, 1912, 

 p. 189. — Lucks, Rotatorienfauna Westpreussens, 1912, p. 125; not Lepadella 

 triptera Ehrenberg, 1832. 

 Lepadella cristata, Harking, Bull. 81 U. S. Nat. Mus., 1913, p. 63. 

 The lorica is broadly oval in outline, slightly constricted near the 

 anterior margin, and truncate posteriorly; its width is three-fourths 

 of the length. The dorsal plate is convex and has a high median 

 keel, prominent at the anterior margin and increasing in height 

 until reaching the middle of the dorsal plate; from this point the 

 height decreases gradually toward the posterior end of the lorica. 

 A large spine is nearly always present on the anterior half of the keel; 

 it is extremely variable in size and form, as shown by figures 8 to 11, 

 and may be completely absent, as in figure 7 ; perhaps the commonest 

 form is that represented by figure 10. The spine is strongly com- 

 pressed laterally; the base is quite narrow and the dorsal edge linear. 

 Longitudinally the base of the spine usually extends about half the 

 length of the lorica; its length, measured from the anterior margin 

 to the tip, may in extreme individuals be almost equal to the length 

 of the lorica, but is more commonly about half the length. The 

 ventral plate is nearly flat, slightly decurved at the edges. The 

 cross section of the body is triradiate; at its highest point the keel 

 is comparatively thin with moderately concave sides. The dorso- 

 ventral depth of the body is one-half the length. 



