564 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



Commission, Woods Hole. The fact that these two were captured 

 in surface skimmings is an indication that this species swims about 

 f reel} 7 at the breeding season. 



As the measurements indicate they are very small and well suited to 

 parasitism upon such small fish. They are also very transparent and 

 might well have been named diaphanus had not that name already been 

 preoccupied. Consequently it makes an excellent species for study, 

 since the internal anatomy can be plainly seen without dissection, and 

 the small size is to its advantage when examined under a high power. 

 It is a very lively species and moves about freely over the body of its 

 host. Like the Argulus found upon the same minnows, this species 

 occasionally forfeits its life when the fish get hungry, and the author 

 lost a fine lot of males and females which were being kept upon Fun- 

 dulus in an aquarium, the fish catching them as they were swimming 

 about. 



CALIGUS SCHISTONYX, new species. 

 Plate VI. 



Female. — Carapace one-sixth longer than the rest of the body, 

 about as wide as long, ovate, strongly narrowed anteriorly. Frontal 

 plates wide and prominent; lunules large, almost circular, slightly 

 projecting. Posterior sinuses rather narrow and somewhat inclined 

 to the median axis; median lobe less than half the entire width and 

 projecting but little beyond the lateral lobes; the latter broad and 

 well rounded (fig. 66). 



The carapace is very peculiar in its grooving; the thoracic area is 

 almost quadrilateral and is about three-fifths of the length and width 

 of the carapace. From each of its anterior corners a pair of parallel 

 grooves extend diagonally forward and outward to the very edge of 

 the carapace. These grooves are close together and each makes a 

 break in the continuity of the carapace margin. This is the only 

 instance within the author's experience, in which an} 7 of the carapace 

 grooves actually reach the margin, and it is very noticeable for that 

 reason. 



Taken in connection with the groove along the anterior border of 

 the thoracic area it forms a joint extending the entire width of the 

 carapace and- separates the head as completely from the thorax as the 

 latter is separated posteriorly from the abdomen. 



The central portion of the thoracic area is raised considerably, 

 leaving a very narrow depressed border around the posterior margin. 

 The line of demarcation between the raised and depressed portions is 

 not parallel with the carapace margin, but on either side forms a 

 straight line inclined toward the central axis and in direct continuation 

 of the posterior of the two inclined grooves already noted. The com- 

 bination of this line of demarcation and the grooves thus produces a 



