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BULLETIN OF THE UNITE!) STATES EISH COMMISSION. 
“Rattulus lunaris” (pi. xiv, figs. 131, 132). 
( Trichoda lunaris Muller, 1776; Rattulus limans Elirenberg, 1838; Mastigocerca lunaris Weisse, 1847.) 
“ Rattulus lunaris’' was evidently described from one of the smaller species of Diurella, but 
the descriptions have been so inexact, and perhaps erroneous, that it seems impossible to recognize 
the animal with certainty. In fact, it is probable that several different species of Diurella , 
inaccurately observed, have been given this name, so that it was really a collective designation, 
which can not be restricted to any particular species. 
Judging from the description and figure of Elirenberg (1838), Rattulus lunaris has a striking 
resemblance to Diurella brachyura G-osse. The form of the body, the position of the foot, the 
length of toe relatively to that of the body, and the unarmed anterior edge of lorica, are striking 
points of similarity. But Elirenberg assigns to this animal two eyes, which, if credited, prevents 
the identification of the two. Elirenberg decidedly emphasizes the presence of the two eyes; names 
the animal “ Brillenratte ” on account of them, and discusses their position, in a way that makes it 
difficult to believe he could have been entirely mistaken as to their existence. A number of other 
investigators, notably Eichwald (1847). Perty (1852). Bartsch (1877), and Wierzejski (1893). have 
reported finding Elirenberg \s Rattulus lunaris, and Eichwald especially mentions that it can be 
distinguished from closely related species by the two eyes. Elirenberg states also that the toe is 
simple and styliform. Two of his figures are reproduced in figs. 131, 132. 
Weisse (1847) describes as Mastigocerca lunaris what he considers to be Muller’s original 
species. Weisse’s animal had but one eye , and he seems to incline. to the belief that the assignment 
of two eyes to this animal by other observers was a mistake. He notes that he himself had reported 
finding Ehrenberg’s Rattulus lunaris, but that after once noticing the single eye he was never again 
able to find specimens with two. But Weisse's description does not help greatly in deciding what 
animal should be called lunaris. owing to the fact that his description was evidently based on 
observation of at least two different animals. He says that some specimens had the toe about one- 
tliird the length of the body, while in others the toe was full half the length of the body. The 
former is represented in his figs. 4 and 5. the latter in his fig. 6. Judging from his description and 
figures, the former may have been Diurella brachyura Gosse, the latter Diurella tenuior Gosse. 
But there is no statement as to the presence or absence of teeth at the anterior edge of the lorica, 
and the figures and descriptions are in other respects also so general in character that it is quite 
impossible to be certain in the matter. 
Taking all together, it seems necessary to let the name lunaris drop, it being impossible to 
recognize any definite species as corresponding to the description given. 
Distemmasetigerum Elirenberg (pi. xiv. fig. 134). 
This animal, from the structure of its toes and its general appearance, seems to belong to the 
Rattulidce, where it would be assigned to the genus Diurella. But the assignment to it of two eyes 
by Elirenberg prevents its identification with any known species. Ehrenberg’s specific characters 
are: Body oblong-ovate; the two eyes red; the toes seta-like and decurved. He mentions the fact 
that it might easily be confounded with Rattulus (lunaris). 
Bartsch (1877) reports this species from Hungary. 
Monocerca valga Elirenberg (1838). 
As noted by Hudson & Gosse (1889), this was apparently a male rotifer of some sort. 
“Rattulus cimolius” Gosse (1889) (pi. xv, fig. 138). 
There is nothing in Gosse’s description to indicate that this animal belongs to the Rattulidce, 
except, possibly, the unsymmetrical trophi. But this is a character which is not at all rare, 
as Lund (1899, p. 70) has observed, in various Notommatadee. For the rest, all the characters 
mentioned by Gosse are quite foreign to the Rattulidce, but are characteristic for some of the 
Notommatadee. The skin is flexible (there being, so far as can be judged from description or 
figure, no sign of a lorica); brain opaque; toes blade-like; there are no substyles; apparently no 
eye; auricles present on corona. None of these characters are found in the Rattulidce, so that it 
seems that there is absolutely no ground for including this species in the present family. 
Gosse found one specimen at Sandhurst, Berks, England; another specimen in a pool near 
Birmingham, England. Glasscott, (1893) reports finding it in Ireland. 
