17 



third, the clypeus. The relation of these parts is remarkably constant in all 

 the Lepidoptera. In the Bombycidse there is a great variation in all the 

 groups; but in the Noctuidse they are very constant. The relative proportion 

 of these pieces is very constant in the Phalaenidse, so much so that they are 

 seldom of much practical use as generic characters. 



The occiput, or base of the head, on the vertex, is separated by suture 

 from the orbits. It is usually very short (antero-posteriorly) in the median 

 line of the head, widening out where it touches the orbits. 



The epicranium is very small and narrow, often not extending on either 

 side to the orbits. It is contracted in front, extending between the insertion 

 of the antennae, and is moderately convex. 



The clypeus occupies nearly the entire front of the head, and is so large 

 as to carry the insertion of the antennas well up on the vertex. It is usually 

 considerably longer than broad, especially in many of the higher genera; 

 while in Euplthccia it is shorter; so, also, in Boarmia. The sides are often 

 parallel, and often also converge a little anteriorly; the base is deeply sinuous, 

 being excavated on each side to receive the antenna 1 . 



How these pieces vary in several of the typical genera may be seen 

 from the following notes and figures, beginning with the lower genera and 

 ascending to the higher: 



Euplthccia mlserulata (pi. G, fig. 19). — In this species, the occiput is longer 

 than usual, and as long in the middle as on the sides, being transversely 

 oblong. The epicranium is equilaterally triangular, though a little shorter 

 than broad. The clypeus is considerably longer than broad, the sides slightly 

 converging. It is rather full on the surface. 



Petrophora diversilineala. — Head much narrower than in the higher sub- 

 families. Eyes full and globose ; both the occipital and clypeal regions more 

 elongated than usual. Occiput long, being one-fourth as long as wide, and 

 of even length throughout, but near the orbits extending anteriorly in a slight 

 point. Epicranium rather small; subtriangular; hinder edge a little more 

 convex than usual. Antennas moderately far apart. Clypeus nearly square, 

 a little longer than broad; sides straight and parallel. No orbital region; 

 front of clypeus well rounded, convex; mandibles well developed; labrum 

 minute; and tongue well developed as usual. 



Hijdria undulata. — In some respects a mean between PetropJiora and 

 Phibalapteryx. Eyes less full. Occipital region not so wide as in Petrophora; 

 ?> v II 



