86 GEO. H. HORN. M. D. 



The sexual peculiarity most numerously observed among the Staphy- 

 lididaj, after the dilated tarsi, is some form of emargination or incisure 

 of the seventh % ventral segment. This is observed in about half of 

 our Cryptobium. 



As the species now stand recorded the following have the seventh % 

 ventral incised or emarginate : sellatwn, cali/ornicuui, Jlaviconie, tu- 

 midiim, pallipes, latebricola, cribratum, serpenfinum, prospiciens, pu- 

 sillum and lepidum. The form of the incisure varies, and will be more 

 fully explained under the different species. 



In the other species not enumerated the seventh ventral is absolutely 

 simple and alike in the two sexes.. These, however, have a special char- 

 acter in fully developed males consisting of a prolongation of the middle 

 of the fourth segment in the form of a lobe extending at times beyond 

 the posterior margin of the fifth ventral. This lobe may be either broad 

 and obtuse at tip or narrow and quite acute according to the species. 

 The first variation observed in this lobe is in a specimen of arizonense) 

 in which the tip is truncate, and the lobe shorter than the fifth ventral* 

 From this the lobe becomes gradually shorter, losing .the long fimbriae, 

 until it becomes barely perceptible in the hind margin of the segment 

 being a little more arcuate. The lobe, in fact, finally disappears entirely. 

 Full series of at least six of our species are before me illustrating the 

 shortening and final disappearance of the lobe, nothing remaining to dis- 

 tinguish the specimens as males excepting the plica or fovea on both the 

 third and fourth segments. We have, therefore, among these species a 

 true sexual polymorphism in the males which would be very confusing 

 and lead to an undue multiplication of species without large series were 

 at hand. 



Near the posterior margin of the third ventral of the male we observe 

 a short transverse plica bearing short erect setae. In several species the 

 plica is reduced to a simple puncture as in ventrole. On the fourth ven- 

 tral there is usually a puncture sometimes large and deep as in pimerianvm, 

 or small as in the greater number of species. Rarely the transvere plica 

 is well marked on both segments. 



As a general rule the size of the head gives no indication of the sex. 

 Males with a well developed ventral lobe have a larger head than the 

 females, while those males with a short or no lobe are not in any respect 

 different from the females in the form of the head. 



The seventh ventral is always simple in the female, and in but few 

 species do we observe a plica, and then on the third segment only. 



