24 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Certain of the new species here described were based upon the exam- 
ination of a single specimen, but of most of them several individuals 
were studied. It is, in my opinion, less adducive to confusion of nomen- 
clature to preliminarily separate aberrant forms; even though only single 
specimens are known, than to class them all under one name. This 
group of worms is difficult of study, the external specific characters are 
few, and it appears that it is a group in which many of the species are 
in process of transformation, judging from their amount of variability. 
Then there are sometimes sexual differences, as well as differences at 
various times of life. Bearing these points in view, I have laid par- 
ticular stress upon the following systematic characters: the superficial 
markings of the cuticle, which have been shown by Villot to present 
exceedingly valuable and reliable characters, though even the surface of 
the cuticle is in many forms subject to individual variation ; the form of 
the posterior end in both sexes ; and, though this is not as reliable as 
the preceding character, the form of the anterior end. The presence of 
median dorsal or ventral grooves along the surface of the body is a less 
reliable character, and still less so is the coloration. The males are 
more easily determined than the females; the form of the tail lobes in 
Gordius and the presence or absence of hairs or spines in their neighbor- 
hood are of much importance ; but in the genius Chordodes the form of 
the posterior end of the male is much more uniform than in the males of 
the former genus. 
A historical review of the previous researches upon the American 
species will be followed by the descriptions of the species examined. 
A. HISTORICAL REVIEW. 
1847. Creplin described Chordodes parasitus, n. sp., from a Brazilian 
Acanthoditis, but his brief description is altogether insufficient for pur- 
poses of identification. 
1849. Gay described from Valparaiso, Chile, a Gordius (G. chilensis) 
as follows : “ Gordius gracilis, cinereo-fuscus, obscurus ; capite nigro . . . 
es de color pardo morenusco oscuro, son la estremidad anterior del cuerpo 
6 la region cefálica negra ; en los manchos la porcion posterior se bifurca 
mucho.” I agree with Camerano (’90) that this diagnosis is wholly 
insufficient. 
1850. Leidy briefly refers a Gordius seen by him to the European 
G. aquaticus. 
