Note identifying insects and remarking on stridulation.
The insect in question is a member of the group Pedinites family Tenebrionidae as defined by Jacquelin Duval in his ``Genres des coleoptères d'Europe''.
In this group the ♂s often differ very much from the ♀s as in Pedinus or hardly at all as in Phylax— stridulation has not been noticed in any member of this group hitherto. I find it in Pandarus & Heliopathes (including olocrates). In Litoborus an intermediate genus where the tarsi are hardly dilated in the ♂—I do not find it. In Pedinus where the tarsi are dilated, I do not find it however— a number of closely allied genera I have not been able to examine.
The insects sent are
Heliopathes gibbus Fabr. Anglia common on the coast
Hel. cribratostriatus Chev Reynosa in Spain
on the Mountains— They seem to squeak very little in nature— at least I have only once noticed it alive & I have taken some thousands—but when dead it is often apparent in the process of pinning
- f1 6529.f1The date is established by the relationship between this letter and the letter from G. R. Crotch, 2 October . Crotch had offered to assist CD in the investigation of insect stridulation after his brother's wedding on 5 October 1868 (see letter from G. R. Crotch, 2 October  and n. 2).
- f2 6529.f2For Pierre Nicolas Camille Jacquelin Du Val's definition of Pédinites in Manuel entomologique; genera des coléoptères d'Europe, see Jacquelin Du Val 1857--68, 3: 271. In Coleopterum catalogus 18 (1910--11): 271, the genera Crotch discusses are in the subfamilies Pedininae and Opatrinae.
- f3 6529.f3For descriptions of Pedinus, Phylax, Pandarus (synonym Dendarus), Heliopathes (synonym Heliophilus), Olocrates (synonym Phylan), and Litoborus, see Coleopterum catalogus 18: 287, 309, 279, 283, 284, and 310, respectively.
- f4 6529.f4CD acknowledged his indebtedness to Crotch for sending prepared specimens of beetles in Descent 1: 379 n. 70.
- f5 6529.f5The name Heliopathes gibbus has not been found; however Phylan gibbus Fabricius is described in Coleopterum catalogus 18: 285. The two genera are closely related. For Heliophilus cribratostriatus (a synonym of Heliopathes cribratostriatus), see ibid. 18: 283.
- f6 6529.f6Crotch may have written in the missing portion that he discovered that the males alone of two Heliopathes species possessed stridulating organs; CD included this information in Descent 1: 383, also writing that on examining the specimens, he found no stridulation rasps in the females of H. gibbus and H. cribratostriatus. CD's notes on these two species are in DAR 81: 175.