56 



It should be added that the identification of M. sordidus, 

 Boisd., seems rather doubtful. Boisduval's description would 

 apply to almost any Mcechidius, but Mr. Waterhouse (loc. cit.) 

 gives some information regarding it which he says is founded on 

 " authentic specimens," but without stating the grounds on which 

 he considers them " authentic." Moreover there is a considerable 

 difficulty in understanding his remarks. Under the heading of 

 M. sordidus he says that that species is one of the commonest 

 Mcechidii in S. Australia, and describes its prothorax as " very 

 slightly narrowed posteriorly, the posterior angles slightly less 

 than right angles." I can at once identify the insect (which is 

 the only common one in S. Australia, and also occurs in Victoria 

 and N.S. Wales) on which that description is founded, but under 

 the description of the next species (M. emarginatus) Mr. Water- 

 house speaks of the " posterior emargination" of the prothorax in 

 " the preceding (species) " and says that emarginatus is closely 

 allied to it. These statements appear quite impossible to recon- 

 cile with each other. I, however, suppose that by some means 

 the place of emarginatus in the memoir was changed after the 

 description was written and that sordidus was not intended by 

 "the preceding," but some other species (perhaps excisus, 

 Waterh.). Therefore I take sordidus, Waterh., to be the insect 

 on which the remarks under the name ^^ sordidtis" were founded, 

 — not that referred to (under the hea^ding '^ emarginatus") as 

 " the preceding." 



Mcdchidius is a genus in which the species are for the most part 

 easily distinguishable inter se by well marked characters, and are 

 readily tabulated. There is however one character that it is 

 impracticable to disregard in a tabulation, but which nevertheless 

 cannot conveniently be used without a few preliminary remarks, 

 and that is the form of the hinder part of the prothorax, which is 

 alike in scarcely any two species of the genus. But the grada- 

 tions of difierence from one species to another are not marked 

 enough to make easy the division of the species into groups 

 founded on this character. In a few species the base of the 

 prothorax is straight or evenly curved, with the sides also 

 evenly curved ; then we find species in which the base is 

 more or less sinuate and the sides evenly curved ; then 

 species in which the sinuation of the base becomes so strong 

 that it should be called rather an " excision" (in some the exci- 

 sion being so angled at both ends that there is an opening for 

 question which is the true basal angle) ; and then species in 

 which the excision takes in more or less of the side of the pro- 

 thorax so distinctly that there can be no hesitation in calling the 

 hinder extremity of the excision the "hind angle of the pro- 

 thorax." I have tried several methods of forming groups on this 



