30 f Jul y> 



bases rather closer together ; a small black point projects in the site of the penis, 

 and the terminal joint of the forceps limb is rather stouter. Can this be an extreme 

 autumnal form of B. rhodani ? 



October. Near Reading. 



20. Baetis tenax, Eaton : Hon., 11G, pi. v, 22, 22a [adult details] ; 



Revis., 164, pi. lxiv, 16 [forceps] (1885 and 1887). 

 Differs from B. vernus in its better developed callus and dcnticulation, its more 

 elongate and less obtuse terminal joint of the forceps limb, and in the basal joiuts 

 of tho limbs being more nearly approximated to each other. 

 Summer. Streams. 



21. Baetis buceratus, Eaton : Mon., 116, pi. v, 23, 23a [adult details] ; 



Revis., 166, pi. lxiv, 19 [forceps] (1885 and 1887). 



Differs from B. tenax and vernus in the greater plumpness of the basal and 

 second joints of the forceps limb, the latter being suddenly rounded off instead of 

 gradually tapering distally ; in the relative bigness of the ovoid terminal joint ; and 

 in the strong decurvature of the last two joints of the limbs, which was so suggestive 

 of a similarity in curvature to bullock's horns held upside down as to determine the 

 name of the species. 



Spring. Near Reading. 



22. Baetis pumilus, Burmcistcr : Mon., 118, pi. v, 25, 25a [adult de- 



tails] ; Revis., 166, pi. xvi, 2de, and lxiv, 20 [adult details] (1885 

 and 1887). 

 Differs from B. niger in having forceps somewhat similar in pattern to those of 

 rhodani, with the terminal joint sub-globular. 



May to October. Streams. 



23. Baetis niger, Linne : Mon., 119, pi. v, 26, 26a [adult details]; 



Revis., 167, pi. xvi, 29/ [forceps] (1884 and 1S85). 



Differs from B. pumilus in the singular form of the forceps. The terminal 

 joint of each limb is extraordinarily elongate and narrow, being nearly of the same 

 width and about three-quarters as long as the preceding joint, these joints resembling 

 tho homologous parts of nabrophlebia fusca. 



Early summer and autumn. Rivers. 



24. Ccntroptilum lutcolurn, Mullcr: Mon., 108, pi. iij 8, and v, 13, 13a 



[adult details] ; Revis., 175, pi. xvii, 30a, and lxiv, 21 [adult 

 details], and pi. xlvi [nympb] (1884, 5, and 7). 

 Hind-wing acuto. Turbinate $ eyes light red. Above the forceps bases 1 is a 

 small acuto median projection. Apt to be confused with Ba'clis binocidatns and 

 Clo'i'on rufulum. - , 



April to November. Streams. 



