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T. obtusa, of which the latter, together with a third species called 

 T. gibba, was first described as a separate species by C. Koch, 1837. 

 In his later works however Koch never mentions T. obtusa and T. 

 gibba, which looks as if he had abandoned the opinion that they 

 are independent species. By Westring T. externa and T. obtusa are 

 distinguished by their different colour, by a difference in the length 

 of the spines on the legs, especially on the anterior tibiae (which 

 spines in T. externa are said to be shorter than, and in T. obtusa 

 of the same length as, the patella), as also by the different hairy 

 covering of the legs. To these Menge adds sundry other distinguish- 

 ing marks, of which one is especially stated to be of easy veri- 

 fication, namely the different form of the strong spine situated at 

 the apex of the male's mandibles, a little above the insertion of 

 the claw. This spine in T. externa is said to be truncated (when 

 looked at in another direction, regularly pointed), and in T. obtusa 

 to be cloven. A large number of specimens may by these criteria 

 be determined as belonging to T. externa or T. obtusa; but this is 

 by no means the case with all. I have female specimens, which, on 

 account of the dark colour of the body, the uniformly dark-brown 

 sternum, the very dark-ringed legs, as also the short, in front 

 more tumid abdomen, I should be inclined to refer "to T. obtusa" 

 but which the spines and hair of the legs show unconditionally to 

 belong to "2\ externa* In most of the males the above mentioned 

 mandibular spine is double-pointed, but the spines on the legs consider- 

 ably shorter than the patella; in others again the extremity of the 

 mandibular spine is so slightly notched, that it is impossible to say 

 to which of these two so-called species the specimen is , in virtue of 

 the form of this spine , to be aggregated. Sundevall ') , L. Koch 2 ) and 

 Keyserling 3 ) , who have described this spine in T. externa (under 

 which name these authors also include T. obtusa), do not mention 

 any other form of it than the double-pointed, which accordingly 

 must be considered as the normal form for the species, and by no 

 means exclusively belonging to T. obtusa. Neither have I been better 

 able by means of the other criteria given by Menge to distinguish 

 with certainty this species from T. externa. The difference in the 



1) Svenska Spindl. Beskr., in Vet.-Akad. Handl. for 1832, p. 257. 



2) Zur Arachniden-gattung Tetragnatha, in Korrespondenz-Blatt d. zool. -miner. 

 Vereins in Begensburg, 16 Jahrgang (1862), p. 79. 



3) Beitrage zur Kenntniss d. Orbitelae, in Verhandl. d. zool.-bot. Gesellsch. 

 in Wien, XV (1865), p. 47. 



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