400 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.46. 



The dorsal plate is strongly gibbous posteriorly, and the depth of 

 the body is almost half the length of the lorica. The anterior edges 

 of the ventral plate curve upward. 



Total length, 152 /x; length of dorsal plate, 96 fi, width, 100 /x; 

 length of ventral plate, 100 ;«, width, 82 /«; width of anterior points of 

 dorsal plate, 32 //, of ventral plate, 53 ix] length of toe without claw, 

 44 n, claw, 8 /<; depth of body, 48 ji. 



Type. — Cat. No. 16522, U.S.N.M., was collected among submerged 

 mosses growing on rocks in a small stream near the Bureau of 

 Standards. 



TRICHOTRIA BREVIDACTYLA, new species. 



Plate 38, fig. 2. 



The body of this species is sHghtly gibbous dorsally and obscurely 

 facetted; the entire surface of the lorica is stippled. The last seg- 

 ment of the body is very broad at the base and tapers rapidly to the 

 foot, so that in dorsal view it appears triangular; on its dorsal side it 

 has a deep depression. The foot has two joints, the anterior one 

 large and conical, the posterior small and cyhndi-ic. The toes are 

 blade-shaped and of moderate length; their upper and lower edges 

 are straight and parallel, the point being formed by a downward 

 curve of the upper edge. In other respects the animal agrees with 

 Trichotria pocillum, T. tetractis, and T. similis. 



Length, 340 /i; toes, 48 /i. 



Type.— Cat. No. 16523, U.S.N.M. 



Two specimens only of this species were collected in the Potomac 

 River. 



DIURELLA PORCELLUS (Gosse). 

 Plate 38, fig. 1. 



A Diurella agreeing in all respects with D. porcellus (Gosse), except 

 in having a very high ridge extending the entire length of the body, 

 occurs occasionally in the ponds at Keniiworth. It is uncertain 

 whether this should be considered a case of dimorphism or whether 

 we are dealing with two species; as an exactly parallel case occurs in 

 the closely related genus Tricliocerca (=Rattulus), it appears inad- 

 visable to give any systematic name to this form, until more is known 

 about the limits of variation in the family. 



I am indebted to Mr. F. R. Dixon-Nuttall, of Ecclcston Park, 

 England, for the figure of this form. 



SPHYRIAS LOFUANA (Rousselet). 

 Plate 37, figs. 4-8. 



Notops lofuann Rousselet, Proc. Zool. Soc. London, 1910, p. 795, pi. 75, figs. 1-3. 

 Sphyrias lofuana Harking, Bull. 81, U. S. Nat. Mus., 1913, p. 96. 

 This species was described by Rousselet from a single specimen 

 found in a plankton collection from the Lofu River, a tributary of 



