ORDER?—ACHREIOPTERA™ Westw. 
In the course of the year 1868, the late Mr. H. Denny placed in my hands for examination a parasitic 
insect, found upon the beaver, which seemed at first sight half-way between a flattened flea and a diminutive 
cockroach, and which appeared to me to belong to none of the recognized Orders of hexapod Annulosa. I 
read a description of this insect with figures, under the name of Platypsyllus castorinus, before the Ashmolean 
Society of Oxford, during Michaelmas Term, November 9, 1868; but, as that Society is very dilatory in pub- 
lishing its Proceedings, I sent a short notice of the characters of the insect for publication in ‘The Entomo- 
logist’s Monthly Magazine,’ which appeared on the Ist of October, 1869, vol. vi, p. 118. By a singular 
coincidence, Herr Ritsema of Leyden published a notice of the same insect on the 15th of September, 1869, in 
the ‘ Petites Nouvelles Entomologiques,’ under the almost identical name of Platypsyllus castoris, regarding 
it as a flattened flea, and consequently as belonging to the family Pulicide—an opinion which the structure 
of the mouth proves to be untenable. Subsequently, Dr. J. Leconte, having carefully examined my specimen, 
came to the conclusion that it was a Coleopterous insect (‘ Nature,’ June 27, 1872), considering the trilobed 
structure of the mentum to resemble that of Leptinus, the lateral processes in which, however, are only narrow 
spines projecting over the gular plate; the antennz resembling those of Gyrinus and Parnus, other parts 
exhibiting an ‘ unmistakable affinity’ with the Staphylinide, Silphide, Corylophide, and especially the genus 
Limulodes of Matthews in the family Trichopterygide, with large and dilated sterna. The same gentleman 
has since obtained other specimens of the insect, and has sent a memoir on it to the Zoological Society of 
London, published in the Proceedings of that Society for 1872. 
The abnormal economy of the insect, its remarkable structure, the apparent want of mandibles (which 
I have failed to discover, although I have dissected several specimens subsequently received in spirits through 
the kindness of Herr Ritsema), our ignorance of its transformations, and the possibility that the creature may 
be Homomorphous in the larva and pupa states, induced me and still induce me to hesitate in regarding it 
as belonging to any of the recognized orders of insects. I therefore here provisionally retain for it the original 
ordinal name which I proposed in ‘ The Entomologist’s Monthly Magazine.’ 
Corpus ovale, valde depressum, coriaceum, setigerum; os (mandibulis?) mazxillis, labio palpisque quatuor 
instructum ; antennz laterales, postice reflexe, tri-articulate, articulo ultimo (ut in Pulice) annulato ; prothorax 
magnus, scutiformis, margine postico sinuato ; mesothoracis scutellum triangulare ; al antic coriacew, plane, 
venis carentes, breves, coalite, basin abdominis attingentes ; sutura recta; ale postice obsolete; sterna omnia 
maxima, plana; pedes cursorii (saltatorii?), tibiis calearatis, tarsis quinque-articulatis, bi-unguiculatis ; meta- 
morphoses ignote; victus parasiticus in Castorem, more Pulicis. 
PLATYPSYLLUS. 
Caput horizontale, semi-cireulare, angulis posticis sub-truncatis, antennis in truncatura insertis; antenne 
longitudine dimidium prothoracis quantes, articulo basali elongato, cylindrico, secundo cyathiformi, extus 
longe setoso, tertio ovali, ex annulis octo (ut in Pulice) formato; Pl. XXXVII, fig. le. Clypeus? (labrum ?) 
semi-ovalis, marginem anticum planum capitis formans. (Mandibularum vestigia nulla inveni'). Maxille motu 
transverso, lobis duobus apicalibus instructs, externo majori, semi-ovali, plano, apice spinuloso, extusque dense 
1 Dr. Leconte states that the mandibles are entirely similar to those of the Corylophides. 
