Oil Aquatic Carnivorous Coleoptera or Dytiscklce. 207 



it is in the Carabiclte, although the temples remain of approximately similar mao-ni 

 tudes in the two families. 



There are but little variations in the structure of the head within the limits of 

 the Dytiscidee ; in Amphizoa the head is not so short in proportion as it is in the 

 other members of the family, and the antennal cavity is not quite so concealed, 

 and the transverse sutures of the under surface are extremely obsolete ; these 

 differences are however but slight, and in other respects the head of Amphizoa is 

 essentially similar to that of the Dytiscidte. 



The most important characteristics of the Dytiscid head besides its short, broad 

 form, are first, its great extension transversely behind the eyes, so that its shape is 

 far fi'om being cylindrical, and second, the great extension of the eyes on the 

 under surface, so that they approach very near to the maxillary cleft : to these may 

 be added as subsidiary, the broad gula, and the existence of the protocranial suture 

 on the under but not on the upper surface. 



In the genus Pelobius we meet however with insects possessing a head dlft'erent 

 from that above described as characteristic of the Dytiscidas ; its posterior portion 

 is cylindrical and not laterally dilated behind the eyes, which are prominent and 

 convex ; there is no jirotoci'anial suture either on the upper or under surface, and 

 the anterior angles of the clypeus are more produced or acute than in any other of the 

 Dytiscidfe : on the other hand the gula is broad, and the eyes extend on the under 

 surface near to the maxillary cleft, these being points characteristic of the Dytiscidse. 

 Some of the members of the Pseudomorphini, one of the aberrant groups of the 

 Carabidfe— ajiproach the Dytiscidse in several details of the structure of the head ; 

 the antennse in Silphomorpha — one of the genera of Pseudomorphini — are inserted 

 far on the under surface of the head ; the eyes are not prominent and approach on 

 tlie under surface near to the maxillary cleft ; and the protocranial suture is distinct 

 on the under surface but not on the upper surface ; while the general form of the 

 head is broad and flat, and departs very far from the cylindrical form ; it is how- 

 ever comparatively narrow behind, the cheeks are very much longer than the 

 temples, and there is a very deep and remarkable antennary groove between the 

 eye and the maxillary cleft : this head, therefore, though far from agreeing with 

 that of the Dytiscidse, has the insertion of the antennse, and the development of 

 the antennary groove an exaggeration of what exists in that family, and is thus in 

 these points more different from the normal Carabidre than are the Dytiscidse. The 

 Haliplides have a head which is remarkably deep in the vertical direction, the 

 insertion of the antennse is conspicuously exposed on the upper surface of the head, 

 there being no trace of that folding under of the antero-lateral portion of the 

 epicranium so universal in the Dytiscidse (but which however is wanting in Eretes); 

 the protocranial suture is distinct on the under, wanting on the upper surface, the 

 cheek is very short, the temple large, and the gula broad, characters of the 

 Dytiscidse : and the submental piece (piece pi-ebasilaire) is of large size, although its 



