Zool.-Vol. i.] MONTGOMERY— GORDIACEA. 339 



would seem to be frequent in C/iordodes, at least I find 

 them in my species of C. morgani, C. -puerilis, and C. albi- 

 barbatus, though not in C. furnessi. 



General diagnostic characters. — The union of the follow- 

 ing characters serves to distinguish this from any other 

 North American form : the low aeroles with the remark- 

 able interareolar pits, the attenuation of the anterior portion 

 of the body, and the black mouth spot. The females of 

 this species may easily be mistaken for females of G. den- 

 sarcolatus Montg., since in some specimens of the former 

 the interareolar pits may be very few in number (or entirely 

 wanting ?). But the form of the posterior end is a good 

 distinguishing character: in the female of C. occidentalis it 

 is enlarged — somewhat knob-shaped, while in the female 

 of G. densareolatus it is not of greater size than the preced- 

 ing portion of the body ; there is at least no difficulty in 

 distinguishing them when one has a series of specimens of 

 both before him. 



Key to the Species of Gordiacea of the North 

 American Continent, North of Mexico. 



I . Posterior end trilobed .' . . . Paragordius varius (Leidy), 2 . 



II. Posterior end bilobed, spirally inroWed. .(Paragordius and Gordius, S S ). 



A. A sharp, V-shaped cuticular ridge behind the cloacal aperture. 



a. The cuticle dotted with white spots. . Gordius aquaticus Linn., $ . 



b. The cuticle not dotted with white spots. 



1. A parabolic line of hairs on the tail lobes. 



G. a. difficitis Montg., $ . 



2. No line of hairs on the tail lobes. .G. a. robust us (Leidy), $ . 



B. No sharp, V-shaped cuticular ridge behind the cloacal aperture. 



a. A longitudinal line of long hairs on each side of the cloacal 



aperture G. lineaius Leidy, $ . 



b. No line of long hairs on each side of the cloacal aperture. 



1. Head end obliquely truncated. 



Paragordius varius (Leidy), S . 



2. Head end not obliquely truncated. 



a. Conical spicules behind the cloacal aperture. 



1. Tail lobes short, nearly conical. 



Gordius densareolatus Montg., £ . 



2. Tail lobes nearly cylindrical. 



G. longareolatus Montg., S . 



