334 Mr. A. E. Verrill on new American 



do not live in the water which is undergoing the first stage of 

 concentration, but only in the pans of concentrated brine con- 

 taining about " a quarter of a pound of salt to the pint." 



Our A. gracilis can exist without apparent inconvenience 

 when the water in which they occur is diluted with an equal 

 bulk of fresh water, as well as when it is much concentrated 

 by evaporation. The water in which they were found varies 

 in density from 1-060 to 1-065. 



The genus is characterized by having eleven pairs of four- 

 jointed branchial "feet" or fins along the sides of the body, 

 the middle ones being the longest. Each joint of the " feet " 

 bears flat branchial appendages, ciliated with sharp setffi, as in 

 the other genera of the family. The abdomen is slender, six- 

 jointed, the last joint long, terminated by two small projecting 

 appendages, each bearing from six to ten plumose setas. The 

 first abdominal segment bears the external sexual organs of the 

 male, and a short dilated ovigerous pouch in the female. In 

 the male the head bears in front a pair of large three-jointed 

 hooks or clasping-organs, each of which has on the inner side 

 of its basal joint a small rounded appendage — a pair of slender 

 antennse just behind these, terminated by two or three minute 

 setge — a pair of pedunculated compound eyes — and a dark 

 spot on the middle of the head, which is the remains of the 

 single eye of the young. The mouth below is provided with 

 a broad labrum, a pair of mandibles, two pairs of jaws, and a 

 pair of lateral papillae. In the female the head lacks the stout 

 claspers, which are replaced by a pair of comparatively small, 

 simple, horn-shaped organs. 



Artemia gracilis, Verrill, sp. nov. 



Body slender, in the male about -3 inch long, in the female 



•4. Claspers of the male relatively long and powerful ; first 

 joint thickened, with a distinct angle at the articulation on the 

 outside, and a short, rounded, nearly semicircular process on 

 the inside near the base, about its own diameter from the base; 

 second joint broad, flattened, continuous with the third joint, 

 strongly curved, outline nearly regularly convex on the out- 

 side, until near the middle it suddenly bends inward, forming 

 an obtuse angle, beyond which the outline is concave to the 

 last articulation, where it becomes again convex, forming on 

 the last joint a slight rounded angle ; the inner edge is nearly 

 straight or but slightly concave to the last articulation, where 



10° to 15°= 1075 to 1-117. A brine liaving a density of 1-020, \vliich is 

 nearly that of sea-water, contains about 2'766 per cent, of salt ; one of 

 1-160 contains 21-219 per cent; one of l-07o about 10-279 per cent.; 

 1117 about 15-794 per cent. 



