62 PROCEEDINGS OF THE NATIONAL MUSEUM Vou, 97 
eye to that of the other). The degree of divergence of the anterior 
inner margins of the eyes, dorsal to the antennal sockets a distance 
about equal to the radius of the eye, was found to be a useful character. 
The frons was measured at the level of the antennae. The frons is 
often much hollowed, the concavity being, in the forms here studied, 
a measure of the relative size of the eyes to the head as a whole, as 
is usually also the degree of divergence of the interocular margins 
(which is in general greater, the smaller the eyes). The reader should 
recall that the size of the eyes in most male fireflies greatly exceeds 
that in the female, so that the frons usually differs markedly in shape 
in the two sexes. 
A valuable key character, used also by Barber, is the coloration of 
the two small, polygonal, basolateral mesonotal plates (pl. 3, fig. 21, 
MP) situated anterolaterally to the scutellum (SC) in the space 
between the pronotum (P£#) and the articulations of the elytra (ZL) 
and usually partly covered by the hind margin of the former. 
In Photuris, Photinus, and Presbyolampis there often occurs one or 
two robust conical sclerotized elongated spurs, movable in fresh 
material, which originate in the tarsal socket behind and _ project. 
distally beyond the ventral surface of the distal end or rim of the 
tibia (pl. 2, fig. 16). These spurs, which are to be distinguished from 
those occurring in Diphotus and Microdiphot (pl. 2, figs. 17-19) de- 
scribed below, are prominent in some species of Photinus, but in others 
they are so inconspicuous as to require exhaustive microscopical 
search. The spurs were studied carefully in all species where a large 
series was available, particularly in Photinus pallens (Fabricius, 1798) 
and Photuris jamaicensis EK. Olivier, 1886, where they are very promi- 
nent, and their distribution was found to be absolutely constant intra- 
specifically not only as to over-all pattern but also as to position of the 
individual spurs. Moreover, male and female were found to show the 
same pattern. I feel therefore that the distributional pattern of 
tibial spurs, since it differs in different species, is a useful specific 
character. However, it must be confessed that in species which are 
very small or in which the spurs are difficult to distinguish from 
ordinary hairs because of similar coloration (e. g., P. lewisi) there 
occasionally appear to be discrepancies in distribution both between 
different individuals and between the two legs of a pair. 
The shapes of the maxillary and labial palps are quite distinctive 
and could probably be used as specific characters, but for lack of 
space for illustrations I have used only their coloration. The terminal 
segment of the larger maxillary palp is usually subconical with one 
side produced to an edge, whereas that of the labial palp varies in 
shape from rectangular (e. g., in Photinus nothoides) through triangular 
or hastate (e. g., P. elisabethae) to mitten-shaped (Diphotus mast). 
