506 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ik 



than the central segment, although rarely it is only slightly longer 

 (macrophallus) . Its length may be less than, equal to, or greater 

 than the combined lengths of the central and apical segments. The 

 central segment may be slightly to considerably longer than the apical 

 segment. In some species having short palpi, the apical segment is 

 extremely short. 



In arcanellus, a species exhibiting an intermediate type of palpi in 

 which these organs recurve back over the head and extend partially 

 onto the dorsum of the thorax, the relative lengths of the denuded 

 segments are nine for the basal, seven for the central, and five for the 

 apical. However, with its long scales included, this apical segment 

 has a relative length of approximately ten, illustrating how the elon- 

 gate terminal vestiture may increase the apparent length of the labial 

 palpi. There is no morphological distinction between the short and 

 the intermediate types of palpi, and some transitional forms occur. 

 However, most species not having elongate palpi fall into the one type 

 or the other, and the types are used here as a matter of convenience. 

 Palpi of intermediate length are to some extent associated with setose 

 compound eyes. Short palpi are normally associated with naked 

 eyes, although there are a number of exceptions. 



Among the species of Acrolophus the vestiture of the labial palpi 

 ranges from rather sparse to very dense, short to elongate, and fairly 

 smooth to rough or somewhat tufted. The scales themselves vary 

 from very slender and hairlike to very broad and spatulate, with both 

 types commonly occurring in one species. The slender scales are 

 typically simple, while the spatulate scales may have their apices 

 simple, bifid, or trifid. The scales are variously colored, and a single 

 scale may exhibit two or three different colors. In such cases, these 

 colors may blend gradually into one another, or each may be rather 

 sharply limited to a definite portion of the scale. 



THE COMPOUND EYES 



Unlike the labial palpi and antennae, the compound eyes exhibit 

 almost identical form and vestitm'e in both the male and female of 

 any one species. The eyes vary from fairly large and prominent 

 (protruding) to medium-sized and partially concealed (retracted). 

 T^^pically circular, they are somewhat elliptical in some species; and 

 like those of the majority of nocturnal motlis, they possess many 

 facets. Many species have lashed eyes, with bristles or lashes, which 

 arise around the edge of the eye and curve over it, and are commonly 

 concentrated along the anterior and posterior margins of the eye, 

 although the entire eye may be surrounded by them. The prominent, 

 anterior tuft of lashes in both sexes of arcanellus furnishes an excel- 



