42 Trans. Acad. Sci. of St. Louis. 



sensibly narrowing behind the eyes, so that they would seem 

 to be almost subspecifically distinct, and, if seen in the ex- 

 tremes alone, might be considered specifically different ; I 

 notice the same variability, however, in specimens of texanus 

 taken at Galveston. 



The two species anceps and vitatum* of Horn, — the only 

 other members of the genus thus far described — are not repre- 

 sented in the material before me, and I am therefore compelled 

 to omit them from the table ; the former seems allied to fiori- 

 danum and the latter to jnmerianum, but differs from this as 

 well as all other of our species in coloration, being testaceous 

 with the last two abdominal segments black, the usual rule in 

 bicolored species being to have the last two ventrals paler than 

 the others. Anceps is black, shining, with piceous abdomen, 

 robust in form, with unusually large head, and, like vitatum, 

 occurs in southern Arizona. Convergens is by no means 

 identical with Jioridanum, as announced by Horn, the two 

 species differing in the sexual modifications of the sixth ven- 

 tral, the latter being singularly and exceptionally modified in 

 Jioridanum as represented by New Jersey cotypes. 



In this genus there are only two really distinct kinds or 

 classes of males and not three as stated by Horn. The first 

 kind has the lobe of the third ventral present in more or less 

 developed degree, and the second has no vestige of lobe but 

 retains the discal marks as perfectly developed as the first. 

 There is apparently no other differential character, though 

 the two classes of males probably play quite different roles in 

 the life history of the species. If the lobe gradually dimin- 

 ished to comi)lete disappearance, there would manifestly be 

 but one class of males having a very variable appendage, but 

 I have never seen an unlobed male presenting any trace of the 

 lobe, and such traces would undoubtedly be seen occasionally 

 if the lobe disappeared in that manner. We are therefore 

 led to the conclusion that there is only a certain amount of 

 variability in the lobe and that the unlobed males must con- 

 stitute a distinct class of that sex — possibly infertile. 



* The siguiflcance of this specific name is somewhat obscure. Its repe- 

 tition several times would seem to show that it is not a misprint for 

 vitiatum. 



