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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Bory de St. Vincent at about 1 lie same time (1824) described under the name 
Diurella tigris the animal which I describe below as Diurella porcellus Gosse. As 
the specific name tigris had already been used by Mil Her for a member of the same 
genus, it can not persist. But the generic name Diurella is the first one given to 
one of the Raltididce having nearly equal toes; hence this name has the priority for 
the genus so distinguished. 
We find, therefore, that the generic name Battulus is to be used for the species 
having one very long toe; Diurella for those having two short, nearly equal, toes. 
In 1830 Ehrenberg founded Hie genus Mastigocerca for RaUulus carinatus, while- 
placing the species raff us in Bory’s genus Monocerca. The names Mastigocerca and 
Monocerca have since been much used, owing to Ehrenberg’s great authority; they 
are both, however, merely synonyms of Rattulus. The name RaUulus Ehrenberg 
restricted to a small organism which lie identified with Muller’s Trichoda lunaris, 
and to which he attributed, rather emphatically, two eyes, a character not known at 
present to be possessed by any of the Rattulidce. 
Eichwald (1847) founded the genus Bothr icWerca for one of the Ratiulidce, 
apparently belonging to the genus Diurella , though his account is so vague that the 
animal can not be identified. In any case Bothriocerca is merely a synonym. 
Dujardin (1841) included Diurella tigris Muller in his new genus Plagiognatha, 
a genus containing a heterogeneous group of organisms, supposed to resemble each 
other in their jaws. This genus was not a natural one and must be given up. 
Schmarda (1859) founded the genus Heterognathus for certain species, part of 
them at least belonging to I lie Ratiulidce — apparently species of the genus Diurella. 
The type of this new genus had two equal toes, and was probably Diurella tigris 
Muller. If we are to classify in a genus by themselves the species having equal 
toes (thus following Gosse), this genus would have to receive, according to the laws 
of priority, the name Heterognathus Schmarda. 
In 1886 Tessin gave it as his opinion that the Ratiulidce could not be distinguished 
into well-defined natural genera, RaUulus gracilis Tessin forming a connecting link 
between Monocerca ( Rattulus ) and Diurella. He therefore united all the species 
in the new genus Acanthodaciylus. The giving of a new name was of course an 
unjustifiable proceeding, even granting the truth of Tessin’s contention. If all the 
Ratiulidce are to be united into a single genus, the name Rattulus undoubtedly has 
the priority. Moreover, the name Acanthodaciylus was already preoccupied, in the 
Reptilia (See Hoffman, in Bronn’s Klassen nnd Ordnungen des Tliierreichs, Bd. 6, 
Abth. 3, p. 1089). 
Finally, in 1889, Gosse, in Hudson & Gosse’s Monograph of the Rotifera, distin- 
guished genera as follows: To the species with one long toe was given Ehren- 
berg’s name Mastigocerca. The -genus Rattulus was given an entirely new sense, 
different from that in which either Lamarck, Bory, or Ehrenberg had used it. In 
it were placed the species having two equal toes (including some species which 
clearly do not belong to the Ratiulidce- at all). Finally, the genus Ccdopus was 
founded on the basis of a peculiar structural characteristic, which Gosse thought 
he had discovered in some of the species of Diurella. Gosse thought that the toes 
in Diurella porcedus Gosse, D. tenuior Gosse, D. cavia Gosse, and D. hrachyura 
Gosse consisted of “one broad plate with another laid upon it, in a different 
plane,” and on this feature he founded the genus Ccdopus. As has been repeatedly 
