40 Transactions of the Society. 



the adult will be very dark the full-o^rown nymph is generally 

 darker than the equally mature nymph of a species which will, 

 when perfect, be comparatively light; amongst the Ortbatidse, 

 probably the perfect creatures of the genus Nothrus are lighter 

 and softer than those of any other genus, and one would therefore 

 expect the nymphs to be very light-coloured and soft ; this expectation 

 is confirmed by fact in all known instances, subject to the question of 

 the species I am now about to discuss. The genus Nothrus is one in 

 which the adults are tridactyle with homodactyle claws ; now every 

 known larva and nymph of the family Orihatidm is monodactyle, 

 but the adults vary according to genus (in Nicolet's classification) ; 

 four only of Nicolet's genera are monodactyle, the others (as 

 defined by him) being all tridactyle, and Nothrus is one of the 

 latter group ; moreover, Nothrus is one of those genera in which 

 the nymph usually resembles the perfect form. This genus 

 includes a species called N. palustris, which name was given to it 

 by C. L. Koch,* who says he found it in damp meadows. This 

 species might well be taken as a type of the genus Nothrus (as 

 defined by Nicolet), which is a natural group ; it presents all the 

 characters in a high degree. Included in Koch's genus Nothrus is 

 another species, N. histriatus,^ which appears to be properly classed 

 as a Nothrus. Nicolet, however, figures | what he says is Koch's 

 N. histriatus ; it seems to me entirely difi'erent, and does not appear 

 to be properly included in the genus at all ; it is very hard and 

 dark, and has not the general appearance nor the formation of a 

 Nothrus. Nicolet says correctly that his histriatus has only one 

 claw, and then proceeds to say that it is not a perfect form at all, 

 but is the nymph of palustris. There would not be anything 

 surprising in Koch describing as a fresh species what was only a 

 nymph, as he does this with every nymph of the family which he 

 found, but the appearance of the creature is very unlike a nymph, 

 except in the one particular of being monodactyle, and Nicolet 

 evidently felt this, for he expressly says that it might be mistaken 

 for a perfect creature, and, contrary to his usual habit, he states 

 how he knows that it is a nymph. As a rule he does not state how 

 he ascertained a fact, which it seems to me is to be regretted, but 

 here he gives his reason, and it is a convincing one : he says he saw 

 his histriatus change into palustris. The passage is as follows : — 

 " Cette larve, telle que je Vai jiguree, est ci la penultieme mue, ses 

 teguments sont dejd solides, elle pourrait etre prise pour un 

 animal adult, si ses tarses netaient monodactyles. Je ne connais 

 pas son etat primordial, mais fai assiste a sa transformation en 

 Nothrus palustris!' Nicolet's figure and description of his 

 histriatus are both given with his accustomed accuracy, and are 



* Loc. cit., Heft 29, pi. 13. f Ibid., pi. 21. 



X Loc. cit., pi. 7, fig. 7. 



