8 STAPHYLiNiDiE. \_Alcochariiim. 



which is more or less vaguely impressed for its accommodation. In 

 other forms, e.g. Aleochara, it will be found, on the contrary, that the 

 coxa is imhedtled in an abruptly defined cavity surrounded entirely by 

 a well-marked raised margin. Between the extreme forms mentioned a 

 large number of intermediate stages exist, and in the Aleocharinae offer 

 a satisfactory and readily-observed method of differentiating the genera. 

 AVhen the two cavities exist entirely surrounded by a raised margin as 

 in Aleochara, I have used the expression * cavities complete :' the com- 

 pletion is effected on the inner side by a prolongation of the mesosternuni 

 between the coxae meeting a prolongation from the metasternum : these 

 prolongations may be called the mesosternal and metastcrnal processes, 

 and are each defined by a fine raised border. When these two borders 

 do not meet, I have designated the cavities as incomplete, and the space 

 intervening between their extremities I have called the ' intercoxal 

 isthmus :' this intercoxal isthmus is of variable length and breadth, but 

 in calling it * long ' or ' short,' I have always used the words in reference 

 to its extension in the longitudinal axis of the body." 



According to the number of the tarsal joints, the AleocliarinjB may be 

 divided into five tribes as follows : — 



I. All the tarsi S-jointed Aleochaeina. 



II. Anterior tarsi 4-jointed, intermediate and posterior tarsi 5- 



jointed Mtbmedoniina. 



III. Anterior and intermediate tarsi 4-jointed, posterior tarsi 5- 



jointed Bolitochauina. 



IV. All the tarsi 4-joiated Oligotina. 



V. All the tarsi 3-jointed Deinopsina. 



ALEOCHAEINA. 



Tliis tribe contains thirteen British genera : one of these, Gymnusa, 

 agrees with the rest as regards the number of joints in the tarsi, but 

 dilTers widely from them in the form of the labial palpi, in wliich it 

 rather closely approaches Mylhi'na ; in other respects also it is allied to 

 this latter genus and to Deinopsis ; for the sake, therefore, of uniformity 

 these three genera have been described together at the end of the 

 Aleocharinse : the members of the tribe Aleocharina have all the tarsi 

 5-jointed. 



I. Labial palpi of the ordinary form. 



i. Head not, or scarcely, contracted at base ; border of tho- 

 rax strongly reflexed, not, or scarcely, visible if viewed 

 from side. 



1. Thorax very plainly broader than elytra with the 



posterior angles strongly projecting Homceusa, Kraatz. 



2. Thornx not or scarcely broader than elytra (except 



in one or two instances in which the posterior angles 

 are not projecting). 

 A. Palpi with an extremely minute accessory joint ; 

 intermediate coxa? with cavities entirely sur- 

 rounded by a raised margin Aleochara, Grav. 



