NO. 1573. PARASITIC COPEPODS— WILSON. 351 



type of a new genus which he named Gangliopus, but he classed the 

 male with the genus " Nogagus," and gave it the name N. angustulus. 

 The fact that they were found together did not suggest to Gerstaecker 

 that they might be male* and female of the same species, but such 

 seems to be the case as evidenced by the following facts : 



(1) Negative evidence: Each of the two forms is different from the 

 other types of its own sex which belong to this subfamily. Tliis is a 

 necessary preliminary for the formation of any new genus, and the 

 male should differ as well as the female, as we find it actually does 

 in the present instance. 



(2) Positive evidence: The frontal plates and first antennge are very 

 similar in the two forms; the carapace is relatively longer in the male, 

 but this is what would naturally be expected. In both sexes the 

 carapace is narrowed posteriorly. 



Each sex shows three free thorax segments, diminisliing in size 

 backward ; m the female they are armed with dorsal plates, but these 

 are lackmg in the male, which carries but a single pair of lateral lobes 

 on the first segment. 



The genital segment in each is enlarged and quadrangular; it is 

 emarginate m the female and carries a pair of posterior lobes m the 

 male. The four anterior pairs of legs are biramose, the rami of the 

 first tliree pairs two-jointed, the fourth pa^'r one-jointed. The relative 

 sizes are what would be expected m the male and female of the same 

 species, 9 mm. in the female and 7.5 mm. in the male. 



In view of these facts ^^ Nogagus angustulus^'' may be regarded 

 with considerable certainty as the male of Gangliopus jniriformis and 

 we shall have the following genus diagnosis for both sexes. 



Female. — Carapace obovate, strongly narrowed posteriorly; the 

 lateral areas divided by transverse grooves as in EcTitlirogaleus. 

 Frontal plates prominent; posterior lobes short and triangular. A 

 pair of small dorsal plates on each of the three free segments, all 

 lateral, the first pair with a wide interval between their bases, the other 

 two pairs meeting on the mid-line. Genital segment somewhat en- 

 larged, quadrangular, with evenly rounded posterior corners. Sixth 

 thorax segment well separated and carrying a pair of rudimentary legs 

 as in Dinematura. Abdomen small and square, attached by one 

 corner to the sixth segment; anal laminjp minute, attached to the 

 lateral corners of the abdomen, and destitute of set» or spmes. 

 Swimming legs all biramose, rami small and laminate, those of the 

 first three pairs two-jointed, of the fourth pair one-jointed. Rami 

 of the first two pairs armed with adhesion pads; exopods all carrying 

 short, nonplumose spines, endopods naked. Egg- tubes narrow and 

 twice as long as the bod}". 



Male. — Carapace obovate-elliptical; frontal plates prominent; pos- 

 terior lobes long, narrow, and pointed. Free segments transversely 



