ivith some remarks about the Classification of the Dipter 



75 



Limnobina, but, at the same time sixteen-, instead of fourteen- 

 jointed, antennae. Such forms often showed other anomalies besides, 

 such as the presence of empodia, some peculiarity in the pubescence of 

 the wings (AntochaJ, an anomalous venation (Antocha, Orimarpa, 

 Elliftera) etc. As early as 1859 (1. c. p. 200) I have considered such 

 intermediate, synthetic forms, combining the characters of two or 

 more of the large, compact groups, as probable remains of some 

 earlier palaeontological horizons, and I found it expedient to isolate 

 them froin the other groups; later experience has confirmed.me in 

 this opinion. Without entering into this interesting subject now, I 

 will merely say, that if I had followed the advice of my correspondent, 

 and placed JRhamphidia among the true Limnobina, I would have 

 been obliged to drag together with it its congeners Elephantomyia, 

 Tooeorrhina, perhaps also Styringomyia (compare Monogr. etc. IV, 

 p. 102), and thus I would have spoiled the homogeneousness of the 

 section Limnobina, and lost the advantage of having the archaic 

 forms grouped together. I gained that advantage by paying attention 

 to apparently insignificant characters, as the exact number of the 

 antennal joints •->) and the disappearance of the marginal crossvein, 

 characters which in this case proved to be index-characters. 



If index-characters have proved to be useful in the family Ti- 

 pulidae there is no reason why they should not be equally efticient 

 in other families of Diptera. In order to discover them, a more exact 

 comparative study of the dipterological characters in general is ne- 

 cessary. Even in leaving aside anatomy, the external characters 

 of the Diptera have, as yet, been very insufficiently studied. For 

 instance, a complete comparative description of the structure of the 

 external tegumentary skeleton in different families has never been 

 given. When I attempted the study of chaetotaxy I did not find any 

 sufficient nomenclature of the segments of the thorax, and had to 

 begin with introducing one. The structure of the prothorax and 

 metathorax, the connection between the latter and the base of the 

 abdomen, the relation of the dorsal and ventral segments of the ab- 

 domen, the abdominal segments preceding, and those containing, the 

 sexual organs, afford a multitude of characters which have never been 

 sufficiently taken into account. But their study and description 



i) I agree with Verrall (E. M. M. 1887, p._205) in that there is 

 ouly one well-ascertained species of JRhamphidia in Europe. 



-•) Elephantomi/ia has only 15 joints and Toxorrhina, stuntud 

 in its venation, has only 12 joints. Nevertheless there is not the slightest 

 doubt about their relationship to Mhamphidia, which has 16 joints, 

 the normal number for the Limnobina anomala. 



