No. 392.] MWORTH-AMERICAN INVERTEBRATES. 651 
5. Villot: “ Monographie des Dragonneaux (Genre Gordius, 
Dujardin).” Arch. Zool. gén. et expér., Vol. III. 
6. Villot: “ Révision des Gordius.” Annal. Sct. Nat. (7) 1. 
KEY FOR THE DETERMINATION OF AMERICAN GORDIACEA.! 
I. Posterior end trilobed, Pavagordius varius (Leidy), 9. 
II. Posterior end bilobed, spirally enrolled (Paragordius and Gordius), ĝ 3. 
A. A sharp, V-shaped ridge behind the cloacal aperture. 
a. The cuticle marked with large white spots. Gordius aguaticus 
(Linn.), o 
6. The cuticle not marked with white spots. 
1. A parabolic line of hairs on the tail lobes. G. a. difficilis 
(Montg.), ê 
2. No line of hairs on the tale lobes. G. a. robustus (Leidy), 3. 
B. No sharp, V-shaped cuticular ridge behind the cloacal aperture. 
a. A longitudinal line of hairs on each side of the cloacal aperture. 
G. lineatus (Leidy), ¢. 
$. No line of hairs on each side of the cloacal aperture. 
1. Head end obliquely truncated. Paragordius varius 
(Leidy), 
2. Head end not oliha truncated. 
a. Conical spicules behind the cloacal aperture. 
1. Tail lobes short, thick, nearly conical. Gordius den- 
sareolatus (Montg. 
2. Tail lobes nearly SEAR G. longareolatus 
(Montg.), £. 
é. No conical spicules behind the cloacal aperture, tail lobes 
i cylindrical. G. platycephalus (Montg.), 
III. Posterior end spirally inrolled, but not lobed, narrower than the preced- 
ing portion of the body, with a depression or groove on its 
ventral surface. Chordodes, $ ¢ 
A. Cuticular areoles longer than high, on and between them small 
circular pits. Chordodes occidentalis (Montg.), 8 
B. Cuticular areoles higher than lo 
a. Spines on the summits of the highest areoles (papilla). C. 
puerilis (Montg.), ¢. 
b. No spines on the summits of the highest papilla. C. morgani 
(Montg.), ¢. 
IV. Posterior end not spirally inrolled, not lobed, not of less diameter than 
the preceding portion of the body. Chordodes and Gordius, ? 9. 
1 The American Naturalist will undertake to determine and return any speci- 
_ mens that cannot be placed in the keys, and solicits correction and criticism for 
future revision. 
