330 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
25. Rattulus bicristatus Gosse (pi. ix, figs. 77-80). 
Synonym: Mastigocerca bicristata Gosse (1889). 
Distinguishing characters . — This very large species is distinguished from all others by the two 
high dorsal ridges passing from the anterior end backward for about three-fourths the length of 
the lorica. From Rattulus mucosus Stokes, the only other species which has two prominent 
ridges, it is distinguished by the greater height and length of the ridges; these in the last-named 
species extend only about one-half the length of the lorica, or less, and they are much lower than 
in R. bicristatus. The two species differ in many other respects also. 
External features . — The body in side view (fig. 77) is oblong, two to three times as long as 
wide, the dorsal line forming a nearly regular arch from head to foot, the ventral line less convex 
and notched at the junction of the head-sheath with the rest of the lorica. The body is not so 
thick from side to side as it is dorso-ventrally, a dorsal view (fig. 78) showing an oblong form, the 
length about three times the width. 
The whole appearance of the animal is dominated by the two great longitudinal ridges. 
These begin at the anterior end, some distance apart, and extend backward and a little to the left, 
ending about one-third the length of the body from the beginning of the foot. The ridges are 
high, thin at the edges, and grow thicker toward their bases. They inclose between them a wide 
V-shaped trough (fig. 78). 
Within the ridges are broad, well-defined bands of muscle fibers, passing from the upper part 
of each ridge to the floor of the furrow between them. These bands evidently correspond to the 
transverse striations occurring in other species; the fibers are not usually grouped into distinct 
bands, as they are in R. bicristatus. 
The head-sheatli is marked off from remainder of lorica merely by a slight constriction, largely 
confined to ventral side. The ridges continue on liead-sheath to anterior margin. There is a slight 
notch between the ends of the two ridges (fig. 78) . and a very slight one on the ventral side. 
Corona . — The corona is of the usual character. It bears two slender lateral processes (fig. 77) ; 
a medial dorsal process has not been observed. 
Antennae . — The dorsal antenna is situated at the bottom of the groove midway between the 
two ridges (fig. 78). In the retracted specimen the eye appears just in front of it. The lateral 
antennae (fig. 78) are in the usual position, a short distance in front of the base of the foot. 
Foot— The foot is rather large, conical, and so attached to the lorica that it can bend to the 
right and ventrally. but not to the left nor dorsally. 
Toes . — There is a single, very long, curved toe, accompanied by numerous substyles (fig. 79). 
One of these substyles is longer than the others and may represent the rudimentary (right?) toe. 
But the primitive arrangement seems entirely lost, so that it is not possible to demonstrate this or 
to show certainly which of the two original toes is represented by the main one. The length of 
the main toe is in young individuals equal to or greater than that of the body; in larger specimens 
the toe is somewhat shorter than the body. As many as eight substyles can be counted, in favor- 
able specimens, at the base of the main toe; possibly the number is still greater. They are much 
more prominent than in most species, some of them standing at a considerable distance from the 
base of the toe (fig. 79). 
Internal organs . — The eye is situated sometimes at the middle of the brain, sometimes at its 
posterior end. It lies beneath the groove between the two ridges. The trophi are very large and 
strong, and bear many teeth. The left side is less developed than the right (fig. 80). 
Rattulus bicristatus Gosse, owing to its great size, is unusually favorable for a study of the 
viscera, but there are no special features to add to the description given in the general account of the 
anatomy of the Rattulidce (p. 288). 
Measurements . — Length of body, 0.25 to 0.30 mm.; of toes, 0.24 to 0.25 mm.; total, 0.49 to 0.55 
mm. Greatest height of body, 0.10 to 0.14 mm. 
This species was described by Gosse (1889) in the supplement to Hudson & Gosse ’s Monograph 
of the Rotifera. Figures or descriptions of it are also given by Glasscott (1893, poor), Stenroos 
(1898), and Jennings (1900 and 1901). 
Distribution . — In America: This species is not uncommon amid the vegetation of rivers, lakes, 
and ponds. I have found it in the following localities: Put-in Bay Harbor and East Harbor, Lake 
