564 PROCEEDINGS OF THE NATIONAL MUSEUM vol. e* 



ing the fourth thoracic segment. Abdomen elliptical, three-fifths 

 longer than wide with a very shallow posterior sinus, the caudal rami 

 basal. The testes are elongate elliptical and reach the entire length 

 of the abdomen. 



The antennae, mouth parts, and first two pairs of legs are like those 

 of the female. On the basal segment of the third legs in place of the 

 thumblike process of the regular male is a slender, 3-segmented proc- 

 ess which extends along the side of the second joint parallel with 

 the axis of the leg instead of standing out at right angles to it. On 

 the basal segment of the fourth leg at the anterior distal corner is 

 a peg that is pointed instead of spherical and apparently 2-jointed. 

 Total length of female, 5.8 mm. ; of male, 4 mm. 



Bemarks.— This new variety is distinguished chiefly by the heavy 

 spinous armature of the antennae and mouth parts of the female and 

 by the prominent carapace shoulders and the sex armature of the 

 basipods of the third and fourth legs in the male. 



ARGULUS ROTUNDUS, new species 



Plate 27, Figures 116-122 



The type, a single female, U.S.N.M. No. 78901, was obtained from 

 an unknown fish in the Gulf of Mexico in May 1915. 



Female.— CsLrap^ce circular, about as wide as long; posterior lobes 

 elongate and coiled around behind the thorax overlapping the abdo- 

 men. Posterior sinus wide and deep reaching the center of the cara- 

 pace. Kespiratory area consisting of a long outer tract curved to 

 follow the outline of the carapace and a very much smaller ovate 

 inner area set into the inner margin of the larger area near its an- 

 terior end. The smaller area is at right angles to the larger one, 

 its pointed end inward. Abdomen wider than long, its posterior 

 sinus not reaching the center, the sides of the sinus overlapping so 

 that the only opening is at the base where the caudal rami are at- 

 tached and they are more or less invisible in dorsal view. 



In the first antennae the basal segment has a small blunt spine 

 at the proximal posterior corner and a still smaller pointed process 

 at the anterior distal corner. The second segment has a smooth 

 anterior margin without any indication of a spine or knob and its 

 ventral surface is likewise unbroken. The lateral claw is stout and 

 strongly curved and the terminal portion of the antenna is 2-seg- 

 mented and reaches just beyond the curve of the claw. The second 

 antennae are slender and 4-segmented, with a spine on the basal 

 segment and an elongate second segment. The sucking cups are 

 large and so close together that they almost touch on the midline. 

 The supporting rods in the margins are slender, each made up of 

 11 segments, of which the 2 basal ones are a trifle larger than the 



