352 BUI^LETIN OF THE BUREAU OF FISHERIES. 



The proximal one is a curved papilla, solid and thickly covered with short spines; the distal one is a 

 hollow conical papilla, split along its dorsal surface, its free edge and much of its dorsal surface covered 

 with short spines. In the posterior portion of this second basal joint is the usual semen receptacle 

 within easy reach of the peg on the fourth legs (see fig. 17). 



The color of the male is similar to that of the female but paler; the brown on the dorsal surface of 

 the free thorax forms in adults a continuous line over the intestine; testes at first brownish yellow, then 

 light reddish brown, and finally cinnamon brown. The ventral surface of both sexes is pale yellowish 

 white without any pigment. 



The newly hatched larva. — Two females of this species full of ripe eggs were captured July 3, 1914; 

 one of them laid a string of 30 eggs the following night and these all hatched on July 14, an interval of 

 10 days, the water being kept at the same temperature as that in the river (72° F.). This is the shortest 

 incubation period yet observed for any species of Argulus, and since the eggs were kept at the same 

 temperature as the river water it must be close to the normal period. 



The eggs are similar to those of A. maculosus (Proceedings U. S. National Museum, vol. 32, pi. 31, 

 fig. 15), the chief differences being that they are not inclined to one another but are all in the same 

 straight line, and while there are two large jelly masses at the junction of every two eggs there is no 

 row of them standing out like the spokes of a wheel. The eggs were transparent and cream colored 

 when first laid but became opaque within 36 hours, and the eyes appeared on the fifth day. 



The newly hatched larvae are much more active than those of maculosus and swim about rapidly 

 with a steady gliding motion similar to that of the adult. At first they swim largely at the surface but 

 later sink to the bottom. They are much more heavily pigmented than any larvae thus far observed, 

 especially through the center of the carapace and along the midline of the thorax, the pigment being 

 the same color as that of the adult. 



Carapace broadly elliptical, the width to the length in the proportion of 13 to 14; anterior margin 

 evenly rounded and with a scattering fringe of very short hairs, amongst which are one or two longer 

 ones on either side; posterior sinus broad and very shallow; free thorax and abdomen forming a wide 

 triangle, whose base, the second thorax segment, is a little less than half the width and whose altitude 

 is a little more than half the length of the carapace. Abdomen half the width of the last thorax segment 

 and a little longer than wide; anal laminae small and rectangular, each armed with two short spines of 

 about the same length. 



In the first antennse the hook of the basal joint is long and slender and reaches to the base of the 

 terminal joint; the latter is spherical and armed with seven large setae, whose tips reach beyond the 

 margin of the carapace, while all the rest of the appendage is covered. 



In the second antennae the entire endopod projects beyond the carapace , the distal joint of the basipod 

 is twice the length of the proximal joint, the temporary' exopod is curved backward, is distinctly three- 

 jointed, and is tipped with a single short spine. 



The temporarj^ mandibular palps are exactly like those of the maculosus larva, even to the spine 

 connected with their base. The second maxills ("anterior maxillipeds") are also similar and termi- 

 nate in two sickle-shaped claws, of which the dorsal one is armed with three barbs. 



The maxillipeds ("posterior maxillipeds") are five-jointed, the second and third joints armed on 

 their ventral surface with spines and bristles. The first swimming legs have a two-jointed basipod, the 

 distal joint armed along its anterior border with a row of short spines; the exopod is three-jointed and 

 ends in two short spines; the endopod is one-jointed and terminates Ln two long nonplumose setae. All 

 the other swimming legs are uniramose, immovable stumps, each ending in a short and blunt spine. 

 There are no traces of skin glands. 



The eyes are large and close to the lateral margins; the ocelli are also exceptionally large and there 

 are only 10 or 12 in each eye. The pattern of the median eye is also peculiar and very different from 

 that of any other species. The sting connected with the mouth is long and projects far in front of the 

 carapace. 



Total length, 0.66 mm.; carapace, 0.40 mm. long, 0.35 mm. wide. 



Remarks. — This species is fairly common on the gars in the river, and as it was recorded by Kellicott 

 from the Niagara River at Buffalo it is probably as widely distributed as its host. Young specimens of 

 both sexes, fully developed but only 1.50 mm. in length, were obtained in the tow in considerable 

 numbers during the middle and latter part of August in several of the slews and in "Sunfish Lake," 

 near Fairport. 



