THE GENUS DENDROCTONUS. 51 



bristles toward the vertex of the declivity and on the declivity 

 itself, or to fine and coarse long hairs over the entire surface. 



Lateral fold or costal groove (fig. 31, n, o). In the costal edge of 

 the elytron, from near the base^o the median section, there is a 

 lateral or costal groove for the reception, when the elytra is closed, 

 of the corresponding produced -and acute dorsal edge of the epi- 

 sternujn. There is also a deeper and broader groove in the median 

 section of the costal area, for the reception of the produced dorsal 

 edges of hypopleurites 3 and 4. According to LeConte and other 

 writers, this lateral groove is an important subordinal character. 



Sutural tongue and groove (fig. 33, a-f). In the sutural edge of the 

 left elytron there is a deep lateral groove and produced ventral edge 

 for the reception of the corresponding produced lateral edge or 

 tongue of the right elytron, thus forming a tongue and groove suture. 

 Toward the apex both the ventral edge of the left and the tongue of 

 the right are dilated to facilitate the locking of the elytra when they 

 are closed. 



Stridulating accessories. In the male there is a transversely and 

 microscopically sulcated area on the ventral surface toward the 

 suture and apex of each elytron (fig. 33). When the elytra are closed 

 this forms a continuous filelike surface situated directly above the 

 stridulating scraper of the seventh abdominal tergite or propygid- 

 iiun. A peculiar, independent, upward and backward motion of 

 the propygidium brings the scraper in contact with the file, and 

 thus produces a peculiar chirping sound which is quite audible to the 

 human ear. 



The exact location of the organs of hearing in these beetles has 

 not been determined. 



Basal and pleural elements. The basal process, or articulatory arm 

 (fig. 32) of the elytron appears to represent the fused heads of the 

 costa, subcosta, and radial veins. The usual scapular, subscapular, 

 flexor, and medial plates are quite definitely represented, and occupy 

 the same relative positions as in the metathoracic wing. The pleural 

 clavicula are represented in the mesothorax by the clavicle and cora- 

 coidnl processes, which are fused beneath the anterior dorsal angle 

 of the episternum to form the condyles (fig. 19). The clavicle disk 

 is not represented, unless it is by a narrow free piece attached to the 

 costal angle of the elytral process, and represents the parapterum or 

 extensor plate, to which the extensor muscle is attached. 



INTERNAL ANATOMY. 



While some study has been made of the internal anatomy of these 

 he<> ties it has not been sufficient to warrant a detailed discussion in 

 this connection. 



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