170 Mr. H. W. Bates on the Endomychidce of the Amazon Valley. 



15. Cori/nomalus cinctus, Fab. ; Gerstaecker, Mon. p. 162. 



At Obydos ; also at Ega, Fonte Boa, and St. Paulo, on the Upper 

 Amazon. 



Dr. Gerstaecker has devoted much space to the analysis of these 

 two forms with their numerous varieties, and he gives as a result 

 that the latter is always distinguishable from the former by the 

 following characters: — 1. The antennte are always black, with the 

 exception of the first two joints, which are rusty-red ; 2. The disk 

 of the thorax is black, the colour generally being divided into two 

 lateral spots, which, though often notably reduced in size, are never 

 entirely absent ; and, 3. The tibiae are black at the basal and rust- 

 coloured at the apical half. In the typical examples, also, the black 

 colour of the under side of the body, where only the middle of the 

 breast and the anus are red, is characteristic. C. mtemiptus is an 

 abundant species in Brazil, including Para, whence the Berlin Museum 

 obtained its specimens, whilst O. cinctus is found only in Columbia 

 and thence further northward to Guatemala. I believe both will 

 prove to be only geographical forms of one and the same species, as 

 the great majority of the specimens which I obtained in the Amazon 

 region, from Obydos to near the Peruvian frontier, partake of the 

 characters of one and the other — a natural result when two forms 

 are not decidedly distinct, seeing that this district of country lies 

 between the ranges of the two extreme forms. Of eighteen examples 

 now before me, one only agrees strictly with Gerstaecker's descrip- 

 tion of C. interruptus ; it has the thorax, the tibiae, and the imder 

 side of the body wholly red, the first four joints of the antennae are 

 red, and the fifth to the eighth are pitchy. It was taken at Obydos, 

 on the Lower Amazons, in company with numerous individuals having 

 most of the above-mentioned characters of C. cinctus. Of seventeen 

 examples which I refer to C. cinctus, five have the thorax spotless 

 red, the antennae (except the basal two joints) and the base of the 

 tibiae remaining black, as they are in the other twelve. Two or 

 three of the specimens have the sides of the breast, and one also the 

 middle of the abdomen, dusky ; with these exceptions, all have the 

 whole of the under surface of the body clear rusty-red. In none of 

 them is the disk of the thorax wholly black, as in the typical indi- 

 viduals of 0. cinctus. We may conclude, therefore, from these con- 

 siderations, that the two forms are related to each other, not as 

 species, but as geographical varieties. By attending carefully to the 

 geographical distribution of forms, we shall find that there are several 

 gradations of relationship between them, and not merely the two 



