466 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
name of a Linnean species of a family distinct from Zapodide, and was also 
used, by various of the older writers, both specifically and generically. Thus, 
Jacvlvs is a generic term used for the Jerboas by Erxleben (Syst. Nat. 404, 
No. 38) in 1777, long before Zapus hudsonius had been discovered. It 
should, therefore, not have been imposed upon any subsequently determined 
generic type. But even according to the rule, custom or precedent, which 
permits an author who subdivides an old genus to restrict the name of such 
genus to any one of his new genera he may see fit, Jacudus is still inapplica- 
ble to the present genus; for such restriction seems to have been first made 
by Jarocki,* a Polish naturalist, who, in 1821, employed the term Jaculus for 
certain pentadactyle species of Dipodide, the name becoming, at his hands, 
exactly equivalent to the subsequent Adactaga of Fr. Cuvier (Proc. Zodl. 
Soc. 1836, 141), afterward altered, on account of its barbarous character, 
to Scirtetes, by Wagner (Arch. fiir Naturg. 1841, Bd. i, 119). Clearly, then, 
if Jaculus is available for any modern genus, it must be for one of the Dipo- 
dide, and can have nothing to do with the present case. It is as much out of 
the question, in fact, as either Dipus or Gerbillus. 
So far as [ am aware, Jacudus was first used in connection with the pres- 
ent genus by Wagler, in 1830 (Natiirl. Syst. Amphib. u. s. w.). In this 
procedure, however, he was followed by no writers of note until A. Wagner,t 
in his “Gruppirung der Gattungen der Nager in natiirlichen Familien” u. s. w. 
(Arch. fiir Naturg. 1841, Bd. i, p. 119), used ‘‘ Jacudus Wagl.” as equivalent 
to, and instead of, Mériones Cuv. The name, however, did not come into 
general employ in this connection until 1857, when Professor Baird adopted 
it in the same sense which Wagler and Wagner had attached to it; and his 
example has been generally followed by the American school. 
2. The term Meriones was invented by Illiger in 1811 (Prod. Syst. 
Mamm. et Avium, ete. p. 82, No. 32), to cover the Old World species ‘ Dipus 
* Jarocki’s work I have not been able to consult. The title and reference,as given by A. Milne- 
Edwards, after Brandt, are :—‘ Zoologia Cayli Zwiertopismo ogolne. Warszwie, 1821. pl. i, p. 26.” Milne- 
Edwards observes: “ Jarocki réserva le nom générique de Dipus aux Gerboises dont les pattes postérieures 
sont tridactyles, et constitua sous le nom de Jaculus un pouvéau genre pour les especes 4 pattes postéri- 
eures pentadactyles”.—(“ Etudes pour servir Vhistoire de la Faune Mammalogique de la Chine,” apud 
H. Milne-Edwards’s “ Recherches,” ete., tome i, pp. 146, 147. 4to, Paris, 1868-74). 
t Says Professor Wagner (tom. cit. 120): ‘‘ Hinsichtlich der Benennung der amerikanischen Spring- 
miiuse erinuere ich, dass ihnen der Name Meriones, den Fr. Cuvier auf sie tibertriigt, nicht beigelegt 
werden sollte, indem ihn Illiger an Nager der alten Welt vergeben hat; ich bediene mich daher des yon 
Wagler vorgeschlagenen Namens Jaculus.” That is to say, Professor Wagner objects to M. Cuvier’s 
transferring Illiger’s Meriones to the American type, without seeming to be aware that he is doing 
the same thing himself,—transferring Jaculus to this type. 
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