On Aquatic Carnworous Coleoptera or Dytiscide. 207 
it is in the Carabidee, although the temples remain of approximately similar magni 
tudes in the two families. 
There are but little variations in the structure of the head within the limits of 
the Dytiscide ; 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 Dytiscidee. 
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 from 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 different 
from that above described as characteristic of the Dytiscide ; its posterior portion 
is cylindrical and not laterally dilated behind the eyes, which are prominent and 
convex ; there is no protocranial 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 
Dytiscide: 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 Dytiscide. 
Some of the members of the Pseudomorphini, one of the aberrant groups of the 
Carabidee—approach the Dytiscidee in several details of the structure of the head ; 
the antennee 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 
the 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 Dytiscidze, has the insertion of the antenne, 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 Carabide than are the Dytiscide. The 
Haliplides have a head which is remarkably deep in the vertical direction, the 
insertion of the antennee 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 Dytiscide (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 
Dytiscidee : and the submental piece (piéce prebasilaire) is of large size, although its 
