540 PROCEEDINGS OP THE NATIONAL MUSEUM. vol.51. 



Metopidia quadricarinata Stenroos, Acta Soc. Fauna et Flora Fennica, vol. 17, 



No.], 1898, p. 165, pi. 3, fig. 2. 

 Metopidia ohlonga v. Hopsten, Ark. Zool., Stockholm, vol. 6, No. 1, 1909, p. 63, 



text figs.— Lie-Pettbrsen, Trom80 Mus. Aarah., vol. 33 (for 1910), 1911, p. 67.— 



DiEFPENBACH, Susswasserfauna Deutschlands, pt. 14, 1912, p. 191, text fig. — 



Lucks, Rotatorienfauna Westpreussena, 1912, p. 119, text figs.; not Squamella 



ohlonga Ehrenberg, 1834. 

 f Metopidia similis Lucks, Susswasserfauna Deutschlands, pt. 14, 1912, p. 191, 



text fig.; Rotatorienfauna Westpreussens, 1912, p. 119, text fig. 

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

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

 Metopidia patella Iroso, Atti R. 1st. Incorr. Napoli, vol. 64 (for 1912), 1913, p. 



474. 



The outline of the lorica varies from nearly circular to moderately 

 elongate oval and ovate, the most common forms being those of fig- 

 ures 1, 8 and 9; the width varies from two-thirds to four-fifths of the 

 length. The dorsal plate is strongly convex and its edges overhang 

 the nearly flat ventral plate; over the foot groove it is occasionally 

 marked with two or four indistinct longitudinal folds or ridges, sel- 

 dom found in the narrower specimens, but apparently constant in 

 the widest specimens. On this pecuUarity Stenroos's Metopidia 

 quadricarinata was founded; it appears to be an individual rather 

 than a specific character. The dorso-ventral depth of the body is 

 about one-third the length of the lorica and nearly constant for all 

 varieties, whether narrow or wide. 



The width of the anterior opening is about one-fourth the length 

 of the lorica. The dorsal sinus is broadly U-shaped and its depth is 

 about one-half the width. The ventral sinus is approximately V- 

 shaped, its sides shghtly outcurved and the posterior angle rounded ; 

 the depth is a little less than the distance between the anterior points. 

 Both dorsal and ventral plates have a stippled collar, strongly marked 

 on the median line and disappearing gradually toward the sides. 



The foot groove is approximately one-third the length of the lorica; 

 its outline varies from nearly parallel-sided to shghtly ovate. The 

 posterior emargination is usually very shallow, with rounded corners, 

 but varies to the lunate forms of figures 2 and 12, plate 90, with obtuse- 

 angled points. The edges of the foot groove project shghtly below 

 the surface of the ventral plate as low ridges. 



The foot is fairly stout; the first and second joints arc very short 

 and of equal length; the third joint is somewhat longer and has a 

 sensoi-y pit on its dorsal side. The toes are about one-third the length 

 of the lorica; they are shghtly decurved, with a certain amount of 

 individual variation, and taper to fine points, the anterior half a 

 little more rapidly than the posterior portion. 



Total length, 135-145 m; length of lorica, 100-108 m, width, 65-90 

 /x; anterior points, 25-27 m; depth of dorsal sinus, 12-14 fx, of ventral 

 sinus, 18-20 /x; length of foot groove, 30-34 /x, width, 18-20 m; 



