39 14 Proceedings of the Roijal Irish Academy. 



Sub-fam. Sperchoninae. 

 Sperchon brevirostris Koeuike var. pachydermis Piersig. (Plate II., fig 18.) 



Abundant under stones in a stream on the lower slopes of Croaghpatrick ; 

 Bunowen stream, where it flows from Lugaloughaun, near Louisburgh, 

 July, 1910. 



The specimens from these and from other Irish localities do not 

 altogether agree with Dr. Koenike's description of S. brevirostris. They 

 are rather to be referred to the form described by Dr. Piersig as 

 S. pachydermis, which is, I think, a variety of Dr. Koenike's species. 



The Irish form is large, ovate in shape, and with prominent shoulders. 

 The epidermis is remarkably thick, and there are strongly developed dermal 

 glands, the arrangement of which is well shown in Piersig's figure (18, tig. 185a). 

 The body is covered with low rounded papillae, which are often a little more 

 prominent on the front margin; the only sharply pointed ones are on the 

 anterior side margins. 



The palps are also somewhat different; they are longer in the variety, 

 and the chitinous peg on the ventral side of the second segment is a little 

 longer. (PI. II., fig. 18.) The rostrum of the mouth organs is also slightly 

 longer. 



The only character in which the Irish form would appear to disagree with 

 S. pachy 'dermis is in the structure of the first and second epimera. Dr. Piersig 

 describes the inner ends of these as " nicht durch eine Brucke mit einander 

 verschmolzen " (Tierreich, 1901). In the Irish examples they meet in the 

 middle line, and are often undoubtedly anchylosed posteriorly through a 

 subcutaneous band of chitin. This does not seem to be a character of much 

 importance, especially as the joining of the epimera is not very evident, except 

 in specimens that have been dissected. 



I have sent Irish examples of this mite to Dr. Koenike, and he also is of 

 the opinion that it should be referred to pachydermis, considering that form as 

 a variety of Sperchon brevirostris. I am indebted to him for a loan of his type- 

 specimen of that species. 



In company with the ordinary form of pachydermis, a few specimens of a 

 smaller size and brighter colouring occurred on Croaghpatrick. I think these 

 are the males of the variety pachydermis. The chief difference is in the 

 epimeral region, which is very much larger. The legs, especially the 

 last pair, are decidedly longer and of more robust build, and the palps 

 are also a little longer than in the ordinary form of the female. 



Common in many Irish mountain streams ; examples, in various stages of 

 growth, may be found clinging to the undersides of submerged stones, often 



