IN THE BRITISH ISLANDS. 19 



The posterior wings are darker, and all have, more or less, traces of 

 the dark transverse line which is rarely (if ever) developed ever so 

 slightly in male tridens. The females of psi have the hind wings 

 more distinctly grey and much more mottled with black scales. The 

 fringes of the two species vary, in the posterior wings, in colour, as in 

 the anterior wings, but psi has the black lines running through the 

 fringes better developed than in tridens, which has the posterior 

 fringes, generally, very clear. 



Acronycta, Och. (Cuspidia, Chapman), tridens, Fab. 



As I have pointed out in the previous paragraph, the following 

 notes were made principally from Dr. Chapman's series : " A very 

 large percentage of Dr. Chapman's tridens are strongly tinged with red 

 in both males and females. Specimens of both sexes have the stigmata 

 in contact, others have them separate ; others have them joined by a 

 short, fine, black line on the internal edge at about the centre or a little 

 lower. The black basal line instead of being distinctly trifurcate at 

 its point, is occasionally only bifurcate as in psi var. bidens. The bifur- 

 cations at the end of this basal line are really parts of the double transverse 

 line, hence some have two bifurcations at the end, besides the central 

 point. - Some specimens are of a much darker grey than others, but 

 all have an ochreous tint. Some have the abbreviated basal line dis- 

 tinct, some very indistinct, there is also a great deal of difference in 

 the development of the second pair of basal lines. Occasionally 

 specimens have distinct dark shades under the black basal longitudinal 

 line. All have a short dark shade, more or less developed, from the 

 costa to between the stigmata ; all the specimens, too, have a pale 

 wavy greyish line outside the reniform, much shouldered near the 

 costa and edged internally with the ground colour, but outside with 

 darker grey, the outer edge is sometimes developed into a distinct 

 transverse shade or band. A fine black line from the third fringe 

 gemination (counting from the apex) cuts this shade, sometimes ex- 

 tending to the fringe mark. The central line of the i/'-like mark at the 

 anal angle is always well developed, the curved part of the mark 

 depends for the development on the intensity of the external transverse 

 shade ; this central line originates in a double gemination at the anal angle, 

 and generally ends at, or near the inner edge of the inner line bordering 

 the pale transverse line * mentioned above. The 7 dark fringe lines 

 are very distinctly marked in all specimens. The males have very 

 clear white hind wings with faintly marked nervures and lunule. A 

 very fine ochreous line borders the posterior margin, in which are 

 placed about 8 dots between the ends of the nervures ; a few males 

 show traces of a transverse row of dots on the nervures and parallel to 

 the hind margin where the transverse shade exists in the females. The 

 hind wings of the females vary from white with slightly grey nervures 

 (darker on the outer margin) and faint traces of a parallel shade and 

 lunule, to wholly grey hind wings with very distinct darker grey 

 nervures (blackish on the outer margin), a distinct transverse line 



* In psi this central line generally passes through a considerable distance 

 beyond the second line. 



c2 



