THE CANADIAN ENTOMOLOGIST 211 



ON THE USE OF THE NAMES LACHNUS AND LACHNIELLA. (HOM.) 



BY A. (.. BAKER, BUREAU OF ENTOMOLOGY, WASHINGTON, D.C. 



In aphid literature ninth confusion has existed in the use of the two names 

 mentioned in the title of this note, and it seems worth while to give the history 

 of the names at the present time in order that entomologists may have the 

 facts before them. 



The genus Lack mis was erected in 1835 b>- ^urmeister, and five rather 

 diverse species were included in the genus, but no type was set. Of these species 

 fagi L. and qnercus L. were removed as the types of other and more recent 

 genera. Various species were from time to time set as the type of Lachnus. 

 These are as follows: 



1840. Aphis rohoris Lin. by Westwood. 



1863. Lachnus pinicola Kalt by Passerini. 



1908. Aphis niidus De Geer by Mordwilko. 



1910. Lachnus punctatus Burm. by Wilson. 



1911. Lachnus fasciatus Burm. by Wilson. 



Now the first three fixations are invalid, since the species were not included 

 in the original genus. The first valid fixation, therefore, is that of Wilson 1910, 

 when he set punctatus as type. According to the rules of nomenclature, this 

 species must remain the type of the genus Lachnus. 



ITnfortunately there is no uniformity of opinion as to what punctatus really 

 is. In other words, the genus Lachnus must remain unknown until punctatus 

 is definitely determined. In 1911 Wilson wrote as follows: "A careful study of 

 Lachnus viminalis Boyer, Boyer's description of that species and Burmeister's 

 description may (?) show that L. viminalis Boyer is identical with L. punctatus 

 Burm. In that case Lachnus will be definitely established with L. fasciatus 

 as type." According to the present writer's reasoning it would be definitely 

 established with L. punctatus { = viminalis) as type, the species set by Wilson 

 in 1910. Later in his 1911 paper Wilson assumed that the two species punctatus 

 and viminalis were the same and, following his argument as just quoted, he made 

 L. fasciatus the type of Lachnus, disregarding his earlier fixation. This was 

 evidently done because L. viminalis had been fixed as the type of Tuberolachnus 

 by Mordwilko in 1908. In a recent paper (1919) Wilson makes the simple 

 statement t\\2t.t fasciatus is the type of Lachnus. 



The writer contends tRat if the identity of punctatus and viminalis is con- 

 ceded to be established, then according to our rules Tuberolachnus will become 

 a synonym of Lachnus having the same species punctatus { = viminalis) as type. 

 And this is a species very different from fasciatus. 



The writer holds no brief for either species, but contends that without 

 special action suspending the rules in this case it is impossible to consider /a^a'a^z/^ 

 the type of Lachnus. He is as anxious as any other worker to have the genus 

 Lachnus definitely established, but he feels that if a change of type for the 

 genus is desirable, considering all the facts, it can be had only through action 

 by the authorities properly qualified to suspend the rules. 



The genus Lachniella was erected by Del Guercio in 1909, but no type was 

 set for the genus. In 1911 Wilson stated this fact, and then placed the genus 

 as a synonym of Lachnus in the following way: 



August, 1910 



