244 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



the young female, and commonly bears obscure teeth at the tip. The head is sub- 

 quadrate, with rounded angles. The very large eye is at the extreme front of the head, 

 its diameter greater than the distance between the eye and the posterior margin of the 

 head. Below, the head is straight; the anterior antennae are not especially prom- 

 inent and the terminal spine is inconspicuous. The posterior spine is like that of the 

 female, long and slender and dorsally placed. The abdomen is without dorsal process. 

 Mature specimen 1 millimeter long by 0.5 millimeter deep. 



Closely allied to D. dentata Matile, with which iny friend Professor Birge con- 

 siders it possibly identical. It differs, however, particularly in the form of the head, 

 the beak of which is much more produced backward in dentifera than in dentata; 

 in the somewhat larger eye (especially of the male) ; in the different form and posi- 

 tion of the dorsal angle, and in its evanescent character in the female adult; in the 

 greater length and sleuderness of the posterior spine ; and, notably in the male, in the 

 different armature of the anterior antenna. Dentifera is also without the tliird joint 

 of the swimming hairs of the antenna. 



Pool near Shoshone Lake, Yellowstone Park. 



OSTRA.CODA. 



Cypris barbatua, n. sp. (Plate xxxvn, Figs. 2 and 3, and Plato xxxvni.) 



An extremely large, very hairy, oblong Cypris, with rounded ends and dorsal 

 and ventral margins nearly parallel. Length, 4 millimeters; width, 1.6 millimeters; 

 depth, 2 millimeters. A very little deepest at hind end of hinge margin. (Depth 

 across eye, 95 per cent of greatest depth.) 



Dorsal margin about straight for a great part of its length, the ventral margin 

 very slightly emarginate or sinuate at its anterior third. The anterior end broadly 

 and smoothly rounded, more obliquely above than below, the posterior somewhat 

 obliquely rounded, the ventral margin being thus nearly half as long again as the 

 dorsal. Seen from above the shape is symmetrical, a slender oval, a little more 

 flattened at the sides behind than before; thickest, consequently, before the middle. 



Color a dirty yellowish-brown in alcohol, with a reddish-brown patch on either 

 side above and behind the middle. Surface of valves opaque, very minutely rough- 

 ened, and well covered with conspicuous hairs, which give this Cypris a decidedly 

 hairy appearance to the naked eye. Hairs longest before and behind and length- 

 ening generally towards the margin, where they project as a fringe, the most prom- 

 inent part of which is a row of hairs borne on slender conical tubercles within the 

 margin of the valves. The valves are equal and the shell fairly full, but not plump. 



Anterior antenna with the basal segment obliquely channeled, partially dividing 

 it into two, the distal part of which bears a single bristle on its superior surface, 

 and two long, more slender ones, springing together from the tip of the ventral sur- 

 face. A short, subquadrate second segment bears a single seta, about as long as the 

 segment, on the dorsal surface, near the tip. From the distal end of the following 

 segment spring two long, slightly plumose setse, one dorsal, one ventral, the former 

 much the longer. The fourth segment bears at its tip four long setsc, two of which 

 arise from the ventral angle and two from the outer dorsal. The following segment 

 is similarly armed, and the distal extremities of the sixth and seventh are densely set 

 with long plumose set;e forming a stout fascicle, which extends beyond the end of the 

 antenna a distance equal to the length of the antenna itself. 



