58 SEKKICOENIA. 



groups, in the first of which it is present, and in the second absent. A small number 

 of species (A. squalus &c.) have the posterior ridge represented by an oval swelling. 

 In the following descriptions I have given the direction of the ridge as viewed from 

 above ; in most cases a side-view of the thorax is given on the Plates, showing the curve 

 of the ridge as viewed from the side. 



The elytra have very constantly the sutural area impressed, leaving a more or less 

 clearly defined raised line about the centre of each elytron : this raised line I have 

 called the " subcosta." The apices are often divergent or expanded, but the species 

 with this character cannot well be associated. 



The prosternum is in front furnished with a more or less semicircular projecting 

 piece (" chin-piece "), which furnishes useful specific characters ; the portion between 

 and behind the coxa? (" intercoxal process ") is very often more finely sculptured in the 

 male than in the female, and in the former is frequently pubescent. Posteriorly this 

 process is sometimes nearly horizontal, gradually narrowed to the apex, the apex 

 entering the mesosternal cavity (A. ratus &c). In some species the part behind the 

 coxa? is very obliquely narrowed, leaving a narrow central process (which enters the 

 mesosternal cavity) at a slightly lower level ; in others this narrow central process is 

 still lower, and appears quite distinct from the rest of the intercoxal process. When 

 this is the case I have, in the following descriptions, described only the part which is 

 visible. In every case, however, it is necessary to draw out the process from the 

 mesosternum in order to see its form at the apex. This is easily done by laying the 

 specimen on its back, when in a relaxed state, and pressing the chin-piece while the 

 body is held firmly by a finger of the left hand. With pinned examples it is necessary 

 to hold the specimen firmly between the thumb and first finger while the prothorax is 

 bent back, otherwise the elytra become dislocated from the thorax. 



The metathoracic episterna vary very little in form, but the sculpture and manner in 

 which the pubescence is arranged afford useful specific characters. 



The abdomen has the first and second segments united into one ; in a few species, 

 however, which I have placed at the end of the genus, the division between these seg- 

 ments is well marked by an impressed line. The lateral margins of the segments are 

 slightly incrassate and form a ridge (" lateral carina"). This lateral carina of the basal 

 segment furnishes excellent specific characters : viewed laterally it is always more or 

 less arched at the base, and posteriorly it is sometimes continued in a straight line (recti- 

 linear), as in A. acuductus, A. suMateralis, &c. ; it slightly or greatly alters its direction 

 (angulated) at the point of division between the true first and second segments (as in 

 A. manatus), or has a notch at this spot, and sometimes has a deep semicircular dip 

 down (A. divaricatus &c). In a few species (A. xanthonotus Sec.) the males have a 

 longitudinal punctured or striated impression on the basal segment. 



The following is the arrangement that I have adopted. Many of the species seem 



