From H. W. Bates   28 May 1868

My Dear M^r Darwin

Being our Anniversary week I have been very much occupied, even my leisure hours taken up by foreign Visitors & medallists; otherwise I should have written before to tell you that I went to Janson on Saturday afternoon & looked out a few beetles for you.¹ He wrote the tickets specifying name & sex, whilst I was there & I hope has fixed them to the right specimens. In Geotrupes there is scarcely any external difference between ♂ & ♀ other than a row of denticulations along the under surface of the anterior tibiæ; these tibiæ have the usual row of teeth on the outer edge in both sexes but ♂ ♂ have in addition this row of small irregular sized teeth quite underneath. I picked you two females & one ♂ of one Geotrupes; a ♂ & ♀ Geotr. Typhœus, & ♂ & ♀ Lethrus, a most extraordinary being closely allied to Geotrupes, its habits described (I think) in Kirby & Spence’s “Introduction”. Luckily I found at Janson’s both sexes of Onitis furcifer.² He promised to try to get Chiasognathus for you.³

The Dynastidæ are remarkable for stridulating organs, their classification being founded to some extent on these organs: as an example I send you ♂ & ♀ Oryctes.⁴ Janson is a very good Coleopterist & a very fair dealing man; he will supply you with anything in his power.

Yours sincerely | H W Bates