10 T. THORELL, 
if two different species belonging to the same genus have obtained the same 
"nomen triviale". If several genera be united in one, that one ought to be 
distinguished by the name of one of them (preferably the o/dest), and on no 
aecount be called by a new denomination. And again if one genus be re- 
solved in several, that genus which contains the typical species") of the 
old genus ought to retain the old generic name; the other new genera ei- 
ther receive new names, or (as is preferable) are distinguished by synonyms, 
if such exist, of the genus, at the expense of which they have been form- 
ed.?) Entirely to reject the old generic name and form new names for 
all the new genera that result from the division, is in general a reprehen- 
sible course. An exception may be made of the cases in which the old na- 
me is an ordinary nomen appellativum, which is equally applicable to all the 
species included under the old name, and is or might be used as the de- 
nomination of a whole Order or Class, as is the case e. g. with the name 
Aranea:?) an exception may also be permitted, when the genus divided does 
not constitute any natural unity, 1. e. when there is no species that can be 
considered as typifying it. We cannot therefore complain that such generic 
names as e. g. Monoculus Linn. and Binoculus GEOFFR. have been rejected 
by later naturalists, though we do not mean to maintain that such a step 
was either necessary or deserving of imitation.) 
1) LiNNÉ and Fapricius say the commonest, "vulgatissima": Phil. bot., § 246; 
Phil. entom., 8 30. As however opinions may be divided as to whether a species 
be most common in, or typical of a genus, it seems to me desirable, when a genus 
is divided, and the person, who made the division, has determined for what spe- 
cies he would preserve the ancient name, not to make any alteration in it. Thus for 
example, although the spider called by SUNDEVALL Salticus formicarius is neither the 
commonest species within the old genus Salticus LATR., nor yet typical of that ge- 
nus, still we retain with SUNDEVALL, who was the first who divided the genus, La- 
TREILLES generie name for just that very species. 
2) "Nomina generiea, quamdiu synonyma digna in promptu sunt, nova non fin- 
genda": Lryy., Phil. bot., 8 244. "Antiquum si disjungitur genus, nova nomina effin- 
genda non sunt, quamdiu antiqua adsunt:” FABr., Phil. entom., p. 113, § 28. 
3) It will hardly be questioned that it is better with SUNDEVALL to call the or- 
der of Spiders Aranee than for instance Araneides, an ill-concocted word, that sounds 
no better than for example Avides instead of Aves or Serpentides instead of Serpentes! 
LINNÉ even lays down as a general rule, that "Nomina generica, Classium et 
Ordinum Naturalium nomenelaturis eommunia, omittenda sunt". (Phil. bot., 8 253). This 
rule however must be considered as bearing with a little modifieation: at least a 
generic name cannot (except in the above mentioned cases) be rejected because 
some Class or Order has subsequently received the same appellation. 
4) If, on the division of a genus, the nomen triviale of one of the species 
