Mr. R. M'Lachlan on Chauliodes and its Allies. 35 



IV. — Considerations on the Neuropterous Genus Chauliodes 

 and its Allies; with Notes and Descriptions. By R. 

 M'Lachlan, F.L.S. 



It is by no means an axiom in natural history that the larger 

 the object the easier it is to comprehend its affinities ; and the 

 insects on which I am now about to make some observations 

 exemplify this in a striking degree. The genera Chaidiodes 

 and Corydalis contain some of the largest Neuropterous spe- 

 cies; yet no two genera, perhaps, show less well-marked lines of 

 demarcation or more instability of structure in organs that are 

 generally looked upon as giving tolerably good means for 

 generic diagnosis. It may be of service, therefore, if I pro- 

 pound my views on this subject, deduced from a consideration 

 of the much-increased materials that have now accumulated. 

 For Corydalis the enormously elongated mandibles of the male 

 of most species, as exemplified in C. cornuta^ and for Chau- 

 liodes the strongly pectinated antennae and equal mandibles, 

 as shown in the typical C. pectinicornis^ at one time seemed 

 enough for all generic purposes ; but an increased know- 

 ledge of forms has shown these grounds to be thoroughly 

 insufficient. Thus in Corydalis we find such species as G. 

 Hecate (which cannot be generically separated from G. cornuta 

 without organizing a system of splitting that would retard 

 rather than advance the science) with equally short mandibles 

 in both sexes ; and in Chauliodes the structure of the male 

 antennge is subject to infinite specific variation, these organs 

 being pectinate, foliate, serrate, or simple, according to the 

 species. Looking, therefore, for more stable characters, I re- 

 gard the presence of few or many transverse veinlets in the 

 wings as the most important character, combined with the 

 presence or absence of a sharp tooth at the lower angles of the 

 head, though, as will be shown, this latter is subject to much 

 modification. 



In 1832, G. R. Gray, in Griffith's edition of Cuvier, pro- 

 posed the term Hermes for an insect with simple male antennae, 

 but which can scarcely be considered other than a Chauliodes. 

 In 1842, Rambur, in his ' Histoire des Ndvropt^res ' (Suites h. 

 Buffbn), separated four species under a genus Which he called 

 Neuromus ; two of these are closely allied to Corydalis, the 

 others can be regarded as only forms of Chaidiodes, one of 

 them being identical with Gray's type of Hermes. However, 

 I propose to adopt Rambur's genus for his two most typical 

 species and for allies since discovered. Their relationship to 

 Corydalis is very close, yet they have a facies that separates 

 them therefrom, and the tooth at the hinder angles of the head 



3* 



