ROTATORIA OF THE UNITED STATES. 
75 
F. cilent ata Collins. — McLaren Lake, Oceana County, Midi. ; Chippewa Lake, Mecosta County, 
Mich.; Crooked Lake, Newaygo County, Mich. (Jennings, ’94). Small pond at Cedar Point, San- 
dusky, Ohio (Kellicott, ’97). Swamp near Norwich, Vt. (H. S. J.). 
F. ambiijua Hudson. — Shiawassee River, Corunna, Mich. (Kellicott, ’84 and ’88). Sandusky Bay, 
Lake Erie (Kellicott, ’96). 
F. coronetta Cuhitt. — American species” (Kellicott, ’84). Shiawassee River at Corunna, Mich. 
(Kellicott, ’88). 
F. trilobata Collins. — Pond near Bangor, Me. (J. C. S., ’83, under the name F. trifolium). Corunna, 
Mich. (Kellicott, ’84, as F. trifolium). 
F. regalis Hudson. — Found by Up de Graff at Elmira, N. Y. (according to Kellicott, ’84). 
Acyclus inquietus Lcidy.— Schuylkill River, near Philadelphia (Leidy, ’82). 
APSILUS Metschnikoff. 
(Plate 14, figs. 1 and 2.) 
What seems to he the young free-swimming form of a species of this genus was found sparingly 
amid Lenina, Spirodela, and TYolffia in the swamp near the United States fish-hatchery, on South Bass 
Island, in July, 1898. It is not possible to determine the species of young specimens from the pub- 
lished descriptions of the members of this genus, because they deal entirely with the adult. In my 
paper of 1894 I assumed that this was A. lentiformis Metsch., that being the only species recognized as 
certainly well established by Hudson and Gosse. But if Stokes (’96c) is correct in his contention that 
four species of the genus are to be recognized, then this may belong to any of them. A thorough study 
of the animal was undertaken, but they disappeared before this was completed; I give my notes and 
drawings, however, so far as they go. A side view, accurate as far as it goes, but not showing all 
details, is given in fig. 1. 
The body is thick and clumsy and slightly curved, so as to be convex dorsally and concave ven- 
trally. It tapers slightly toward both ends, ending in a truncate fashion, at the anterior end in the 
head, at the posterior end in the broad disk which serves as a foot. The head is separated from the 
body dorsally by a slight depression, while ventrally the outline of the body continues uninterruptedly 
into the head. The posterior disk is marked off from the body by a broad shallow constriction. The 
animal is very transparent and entirely colorless, except for the two red eyes. 
The ciliated face at the anterior end is slightly oblique, a non-ciliated part projecting above the 
ciliated portion. The cilia are rather long and seem to form a simple circle, but observations on this 
point are not complete. A large lobed brain lies behind the corona, bearing in front the two red eyes, 
in which crystalline lenses are clearly visible. The head may be extended considerably farther than 
is shown in the figure, or may be entirely retracted. 
The body of the animal is filled with a bewildering confusion of glands, digestive organs, 
muscles, and nerve cords. Much of interest might be brought out by a minute study of these parts; 
1 have seen n n rotifer that appeared so favorable for a study especially of the muscular and nervous 
systems. The figure, accurate so far as it goes, gives an idea of the complex of details awaiting 
disentanglement. I shall not, in the absence of minute study, attempt to interpret the structures 
shown. The prominent trophi lie, as in other members of this genus, at the bottom of a large sac; 
they are of the peculiar form characteristic of the genus. They are shown in fig. 2, plate 14. 
The body wall seems much more complex than is usually the case in the Rotifera. It appears to 
be possible to distinguish four layers, beginning with the outside: (1) A thin cuticula; (2) a thick, 
gelatinous cellular layer; (3) a layer of transverse muscles; (4) a layer of longitudinal muscles. The 
two muscular layers are not completely separated, and some of the longitudinal muscles traverse the 
body cavity, but in a general way the distinction into two layers is evident. The posterior disk is 
retractile into a sort of mantle which partly covers it, and the whole, mantle and all, may be drawn 
within the body. The disk is concave, with lines radiating from the deeper central portion, and is 
ciliated. The movements of the animal much resemble those of Asplanchna. 
Lund (’99) holds that Apsilus should be removed from the Flosculariadce and placed in a separate 
family near the Asplanclinadai. 
The present author (’94) recorded this same form from Lake St. Clair as J. lentiformis Metsch. 
A. vorax Leidy. — Schuylkill River and Fairmount Park, Philadelphia (Leidy, ’57, ’82, and ’84). 
A. bipera Foulke. — Fairmount Park, Philadelphia (Foulke, ’84). Pool at Trenton, N. J. (Stokes, 
’96c). Sandusky Bay, Lake Erie (Kellicott, ’97). 
A. bucinedax Forbes. — In an aquarium at Normal, 111. (Forbes, ’82). Pool at Trenton, N. J. 
(Stokes, ’96c). 
