THE VAKIEGATEE MUD-LOVING BEETLES. 683 



presence or absence of the post-mesocoxal line This is ;m elevated 

 line on the metasternum which "begins at the middle of the hind 

 border of the middle coxa? and extends obliquely backward, joining 

 the suture between the metasternnm and its episternum." The 

 first ventral segment bears a stridulating organ in the shape of an 

 elevated curved ridge which is finely striate transversely, and when 

 rubbed by the hind legs, produces a quite distinct sound. Of the 

 11 species recognized by Horn, seven have been taken in Indiana, 

 while another may occur. 



KEY TO INDIANA SPECIES OF HETEEOCERUS. 



a. Thorax with a pale median stripe; stridulating ridge of first ventral 

 segment complete, forming nearly a semicircle; an elevated oblique 

 line on the epipleura near the base. (Fig. 256, c.) 



1302. AUBOMICANS. 



aa. Thorax without a pale median stripe; stridulating ridge of first ven- 

 tral incomplete, extending from the front angle in a curved line to 

 hind border; epipleura without an oblique elevated line near the 

 base. 



Jj. Metasternnm without a post-mesocoxal line ; elytra never with a spot 

 at base near suture. 



c. Labruni of male narrowed at tip and prolonged forward in a 



process ; size larger, 6 mm. ; elytra obsoletely substriate. 



1303. VENTEALIS. 



cc. Labrum of male not prolonged forward in a process; size smaller, 

 not over 4.5 mm. ; elytra usually distinctly substriate. 



1304. TINDATUS. 



hi). Metasternum with a post-mesocoxal line. 



d. Elytra usually brownish or piceous, always with more or less dis- 



tinct dull yellow spots or markings ; mandibles of male without 

 basal lobe extending over the labrum. 

 e. Elytra without a pale spot at base near suture. 



/. Elytra usually substriate, the pale markings much broken; 

 legs more or less piceous ; larger, 3.5—4 mm. 



1305. BRUNNEUS. 



ff. Elytra not substriate. the markings well defined and broad: 

 legs wholly pale ; length not over 3 mm. schwarzi. 

 ee. Elytra wuth a pale spot at base near suture. 



g. General color of upper surface brownish or pale ; thorax mere- 

 ly slightly darker at middle; mandibles of male with an 

 angulate basal lobe on outer side. 1306. collabis. 



gg. General color piceous ; thorax piceous, often sharply bordered 

 with pale; mandibles of male not prominent at base. 



1307. teistis. 



dd. Elytra pale without yellow marks, often with a broad fuscous 

 sutural space; mandibles of male with a basal lobe extending 

 over the base of labrum, 130S. pusillus. 



