NO. 2194. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 71 



EET TO THE SPECIES. 



1. Neck but little enlarged anteriorly and not flexed ; lateral horns at 



rijrht angles to the body axis 2 



1. Neck much enlarged anteriorly, then constricted and flexed at the 



constriction ; tips of the horns turned backwards 3 



2. Lateral horns swollen and bluntly rounded ; proboscis conical and strongly 



tapered (49 mm.)* nodiconiis (Stcenstrup and Liitken), ISGl. 



2. Lateral horns cylindrical and sharply pointed ; proboscis cylindrical or 



spherical (85 mm.) gempyli (Horst), 1S78. 



3. Proboscis short and fully as wide as long; carapace, terga, and sterna 



distinctly visible 4 



3. Proboscis twice as long as wide; no carapace, terga, nor sterna visible 



(26 mm.) inflexus (Steenstrup and Liitken), ISGl. 



4. No constriction behind the legs ; mouth tube turned ventrally ; rami of legs 



armed with setae (13 mm.) scopcli Jungersen, 1911. 



4, A marked constriction behind the legs ; mouth tube in line with head ; rami 



of legs without setae (44.50 mm.) erisialiformis (Brian). 1912. 



4. No constriction behind the legs; mouth tube in line with head; upper lip 



bilobed (22 mm.) lobatus, new species, p. 72. 



Remarl's. — The only i-eason given by Jungersen for establishing 

 the present genus was the fact that it possessed but three pairs of 

 swimming legs, while the closely allied genera possess four pairs. 

 There are, however, several other characters of equal or greater value, 

 such as externally the presence of first maxillae on the sides of the 

 mouth tube in front of the second pair, the softening of the horns and 

 the anterior portion of the thorax, and the persistence of the larvxJ 

 carapace, terga, and sterna. 



Internally there is the peculiar arrangement and character of the 

 chitinogen layer of the body wall, which covers the inner surface of 

 the neck as well as the genital segment, the wheel-like skin glands, 

 and the dorso-ventral flattening of the intestine. Taken accumu- 

 latively these characters establish the genus beyond any dispute, and 

 there should be transferred to it such species as show these characters, 

 or a convincing majority of them. Accordingly that has been done 

 in the key above given. It is worthy of note that Steenstrup and 

 Liitken recognized that the species described by them differed mate- 

 rially from the Lernaeenicus type, and suggested in a footnote the 

 possibility of a subsequent generic separation. Horst stated defi- 

 nitely that his species had but three pairs of legs and an extra pair 

 of mouth-parts, while the " hard chitin parts of the cephalothorax " 

 which he mentioned were probably the persistent carapace, sterna, 

 and terga. Brian showed the same details in the excellent figures of 

 his species, all of which have been confirmed upon a specimen in the 

 United Stales National Museum collection (see p. 72). 



Furthermore this species is not gregarious like Lernaeenicus but is 

 solitary, only a single specimen being found upon a host. 



1 Average total length of species. 



