BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
B. DESCRIPTIONS OF THE SPECIES EXAMINED. 
1. Gordius aquaticus robustus (Leidy). 
Plates 1, 2, and Figs. 13, 16-19 of Plate 3. 
G. robustus Leidy, 756, ’79. 
G. subspiralis Diesing, ’61. 
G. robustus Leidy, Villot, 74. 
? G. violaceus Baird, Villot, ’87. 
? G. aquaticus Linn., Römer, ’95, ’96. 
(Leidy’s 79, types; Leidy coll. no. 5056, Coningo, Maryland.) 
Form. The male more slender than the female, in both sexes the body of 
approximately the same diameter in its whole extent. Head end (Figs. 2, 6, 9, 
10, 11, 17) usually obtuse, especially in the male (Figs. 2, 6, 10), sometimes 
somewhat conical in the female (Fig. 17). Occasionally a slight neck constric- 
tion is present. Usually no median longitudinal grooves are to be seen. In 
some of the larger specimens, especially the females, the whole body is very 
much flattened, and these are apparently individuals which have discharged 
their ova. The posterior end of the female is obtusely truncated (Figs. 7, 8), 
with a faint vertical groove on the termiual aspect; the cloacal aperture is 
terminal, and lies in this groove. Figures 9, 10, show depression on the 
terminal face of the head. 
The posterior end of the male is spirally inrolled (a character of the males 
of all the Gordiacea examined), and is furcate. The tail lobes (Figs. 1, 3-5, 19) 
are short, nearly cylindrical on cross section except that they are somewhat 
concave on their medio-ventral surface, and divergent. The cloacal open- 
ing is round and situated anterior to the point of bifurcation of the lobes. 
On the ventral side of the anterior ends of the tail lobes is situated a more or 
less crescent-shaped transverse cuticular ridge, with posteriorly directed con- 
cave edge. This sharp cuticular ridge is postcloacal. Short branching hairs 
occur on the surface of the tail lobes as elsewhere on the surface of the body, 
but no spicules ; and there is no particular arrangement of the hairs in the 
vicinity of the cloacal aperture 
Cuticle (Figs. 12, 13, 16). True areoles are absent. In most of the speci- 
mens, and especially well marked in the males, the surface of the cuticle is 
marked by very fine intersecting lines, and, at greater distances apart, by 
broader intersecting raised ridges, which are strictly parallel to the finer lines 
which lie in the rhombic spaces demarcated by them, and which themselves 
are formed of bundles of fine lines. These larger ridges are seen with low 
powers of magnification, but higher powers are necessary in order to detect the 
system of finer lines which lie between them. On the cuticle, especially abun- 
dant at the ends of the body, are also seen short, thick, and branching hairs, 
