332 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
“median dorsal cleft’’ which is especially noticeable when the head is withdrawn; this may well 
have been the furrow between the two ridges. It would be very easy to interpret the structure 
as merely a furrow or cleft, the ridges being considered merely the sides of the cleft. Hilgendorf's 
figures are not detailed, so that it is difficult to be certain of the identity of his species; it certainly 
resembles the present one, and his account hardly justifies the founding of a new species. 
Distribution. — This species is one of the most abundant of the Rotatoria amid the vegetation 
of the shallower parts of the lakes. I have found it in the following places: Lake St. Clair; 
Chippewa Lake, Mecosta County, Mich.; Crooked Lake. Newaygo County, Mich.; Round Lake at 
Charlevoix, Mich.; pond at Hanover, N. H.: Huron River at Ann Arbor, Mich., and at the 
following stations on Lake Erie: Put-in Bay Harbor, East Harbor, Long Point (Canada, near 
“The Cottages ’’). 
Stokes (1896) found this animal in a pond near Trenton, N. J. ; Kellicott (1897, under the name 
Mastigocerca bicristata) in Sandusky Bay, Lake Erie. 
New Zealand (?), Hilgendorf (1898) as Mastigocerca. rectocciudatus. 
This species has not yet been recognized in Europe. 
27. Rattulus carinatus Lamarck (pi. xi, figs. 95-97). 
Synonyms: Trichoda rattus vesiculam gerens Muller (1786); Rattulus carinatus Lamarck (1816); Tricliocerca 
rattus G-oldfuss (1820); Monocerca longicauda Bory de St. Vincent (1824); Mastigocerca carinata Ehrenberg 
(1830,1838), and most subsequent authors; Monocerca carinata, Eyferth (1885); AcantKgdactylus carinatus 
Tessin (1886). 
Distinguishing characters. — This species is at once known by the high, thin keel or ridge 
extending somewhat more than half the length of the lorica. It differs from R. lophoessus Gosse 
in the fact that the ridge does not reach the entire length of the lorica. There are also differences 
in the toes and in other features. 
External features. — The body is along oval, widest near the middle and tapering toward both 
ends. The dorso- ventral and lateral diameters are nearly the same (compare figs. 95 and 97). The 
part of the lorica enveloping the head is marked off from the remainder by two slight constrictions. 
The anterior edge of the lorica is cpiite unarmed, and forms a gentle curve, bounding the anterior 
opening, without teeth, angles, or notch. In the ventral region the curve forms a slight shallow 
concavity (fig. 97) ; at this point the lorica can be folded-inward when the head is strongly retracted, 
forming what appears to be a deep, narrow gap. 
The most striking feature of this organism is the very high, narrow ridge. This begins at the 
anterior end, considerably to the right of the median line, and extends obliquely backward and to 
the left (fig. 95), stopping a little behind the middle of the body. The ridge is inclined strongly 
to the right and is marked with transverse striations. These striations appear to be muscle fibers 
passing from the top of the ridge (at its right edge) to the left and downward. When the ridge 
is seen from the side the ends of the fiber bundles show the arrangement given in fig. 97. The 
striations extend on the surface of the lorica some distance to the left of the ridge (fig. 95). 
Corona. — The corona has the usual two arcs of cilia about its dorso-lateral margin and two at 
sides of mouth. There is a short, thick median dorsal process and two slender lateral ones (fig. 97) . 
Antenna. — The dorsal antenna lies on the left side of the ridge, just behind the head-sheath 
(fig. 95). The lateral antennae are in the usual position on the posterior part of the body, the right 
one considerably in advance of the left ( fig. 95 ) . 
Foot. — The foot is of the usual short, conical form. The lorica projects over it dorsally much 
farther on the left side than on the right (fig. 95), so that the foot may be bent to the right or 
down, but not to the left nor up. 
Toes (tig. 96). — The single main toe ( l . t.), representing the left toe of the genus Diurella, is 
an almost straight rod of nearly or qifite the length of the lorica. It is accompanied at its base by 
a number of short scales and spines, one of which, curved so that the tip lies against the main toe, 
seems (by comparison with a number of other species) to represent the right toe (fig. 96, r. #.). 
This is in the present species shorter than one of the substyles proper. 
Internal organs. — The internal organs offer nothing of especial interest except the trophi. 
These are decidedly unsymmetrical, the right malleus being considerably smaller than the left. 
The trophi are essentially like those of Rattulus longiseta Schrank (pi. Till, fig. 72), but with the 
right malleus perhaps a little smaller. 
