464 SEEEICORNIA. 



identified by the form of the genitalia of the males *, figures of these parts of all but 

 one of the Central-American representatives being given on our Plate. The form of 

 the sterna also afibrds good differential characters in certain species, as in P. noctilucus, 

 P. stella, P. radians, &c. The luminous vesicles are raised and very prominent in the 

 first section, flatter and less distinct, rarely obsolete, in the second section. The 

 abdomen is also luminous at the base in various Pyrophori, the membranous luminous 

 space varying in extent according to the species ; but the luminous portion is not 

 visible in dried specimens till the abdomen is removed, it being sometimes reduced 

 (P. radians) to a very narrow space immediately beneath the intercoxal process, and in 

 others (P. strabus) extending across nearly the entire width of the segment. The 

 terminal dorsal segment is probably luminous in P. strabus and others. So far as I have 

 noticed myself, the thoracic vesicles emit a greenish light and the abdomen a reddish 

 light in one of the large species, P. pellucens, a common Central- American insect. 



From Mexico one species only, P. occidentalism is known from the Pacific coast, 

 the others inhabiting the central plateau or the Atlantic slope. No Pyrophorus has 

 been noticed as yet on the Pacific slope of Guatemala. 



These insects, known everywhere in Central America under the name of " Cocuyos," 

 have a much more rapid flight than the luminous Lampyridee, and they emit a steady 

 light, instead of an intermittent one, the light being brilliant in both sexes. They 

 fly for a short time after dark ; the smaller forms may be taken in plenty a little later 

 in the evening at rest upon leaves. 



a. Antennae very short in both sexes, the third joint shorter than the fourth ; 

 prothorax broader than long, with prominent raised vesicles. 

 a'. Propleurse not marked with yellow beneath the vesicles. 



a". The vesicles placed close to the lateral margin, and parallel with it ; pro- 

 sternum declivous behind noctilucus. 



b". The vesicles distant from the lateral margin, oblique ; prosternum not 



declivous behind strabus. V 



b', Propleurse marked with yellow or reddish-yellow beneath the vesicles ; pro- 

 sternum not declivous behind, 

 c". Elytra not more than three times the length of the prothorax j the latter 

 convex. 

 a'". Elytra sharply mucronate at the apex ; prothorax densely punctured, 



the sides rounded or feebly sinuate : size large pellucens. V 



b 1 ". Elytra feebly mucronate at the apex ; prothorax more sparsely punc- 

 tured, the sides distinctly sinuate : size smaller indistinctus. ^ 



d". Elytra more than three times the length of the prothorax, sharply mucro- 

 nate at the apex ; prothorax moderately convex, sinuate at the sides, and 

 densely punctured : size large clarus. 



* Schwarz, Deutsche ent. Zeitsehr. 1892, t. 2, has figured the male genitalia of a large number of Pahearctic 

 Melanotini : these, however, show very little diversity in structure. 



