250 GEO. H. HORN, M. D. 



the posterior margin. This is very evident in Leptodirus and Pholeuon 

 but in the genera in which the closure behind is narrow it is difficult 

 to decide, although it is probable that the prosternum does attain the 

 hind margin of the thorax in them. 



The middle coxae vary, they may be contiguous or separated, in 

 the latter case the mesosternum is often carinate, very obtusely in 

 Plat^choleus, while in Adelops and Bathi/scia it forms a prominent 

 keel-like lamina as in many Hydrophilidae. 



The metasternum is at most of but moderate length, in a large 

 number of the species very short, in the latter case the wings are 

 entirely wanting and in the former very feebly developed. 



The posterior coxoe may be contiguous or separated in the latter 

 case to a variable degree, widely in Leptodirus, by a triangular inter- 

 coxal process as in Platycholeus and Pholeuon or very narrowly as 

 in Bathyscia. 



The legs are rather slender and in many species, especially those 

 living in caves, long and spider-like. The tarsi are always five-jointed 

 on the posterior and middle legs the anterior being often four-jointed 

 either in one Sex as in Pholeuon or in both sexes Oryotus,. The 

 anterior tarsi are more or less dilated in the males and often the 

 middle also, in the latter case the first joint alone is broader, species 

 occur in Colon with the tarsi slender in both sexes. 



The tibial spurs are always slender and in one genus PrionocJiaeta 

 very long and pectinate on their margins, and in the male of Colon, 

 those of the anterior tibiae especially, dentate at the sides. The 

 antennae are variable and are sufficiently described with the genera, 

 very little can be said in a general way excepting that in those genera 

 without eyes the antennae are very long and slender, while in those 

 genera with eyes the antennae are more or less clavate and shorter. 

 The eighth joint is shorter than the seventh or ninth and in most 

 cases also narrower, there being two exceptions only as far as I have 

 seen, the one in Leptodirus with slender antennae, the other in Colon 

 with the clavate form. 



The genera included in this tribe have been more or less widely 

 separated by authors, by giving what seems undue prominence to 

 certain characters to the exclusion of others, but with the arrangement 

 of the genera here proposed the relationship between them seems quite 

 evident, Leptodirus being of course the more aberrant. 



From the curious forms of some of the species of this tribe some 

 erroneous speculations have arisen. 



