844 On Aquatic Carnworous Coleoptera or Dytiscide. 
I. 16.—Genus AMPHIZOA. (Vide p. 318.) 
Three closely allied species form this aggregate. They are insects of somewhat 
elongate, moderately convex form, the outline much interrupted at the junction of 
the thorax and elytra; the colour is an uniform dull black, and the surface is 
sculptured with a coarse, indefinite, but close punctuation. 
The head is rather broad and short ; when in position in the thorax its breadth 
is about one-fourth greater than its length from the front of the thorax to the front 
of the clypeus, and when extracted the breadth is still a little greater than the 
length: the eyes are rather small in proportion to the size of the head, they are 
slightly convex and prominent, and occupy chiefly a lateral position, their encroach- 
ment on the area of the upper and undersurfaces being but small. The clypeus is 
separated from the posterior part of the head by a fine suture, distinct across the 
whole width of the head, the clypeus has about twice the area of the exposed 
portion of the labrum, and is quite continuous with the plane of that part; the 
anterior angle of the clypeus is not folded under in front of the antennal cavity. On 
the under surface the transverse sutures on the lateral portions of the head are very 
difficult to trace. The mentum is united with the base of the head by a very fine 
nearly obliterated suture, and is extremely large, and extends forwards quite as far as 
the front of the labrum, the mandibles and maxille being completely covered by its 
large lateral wings; the outer lobe of the maxilla is curved and palpiform, but is 
not divided by any articulation. 
The antenne are short and stout, and of simple construction, their basal joints 
are punctate or porous; this punctuation becomes more indistinct on the terminal 
joints so that the outer ones are nearly smooth and shining ; there is no pubescence 
to be seen on any of the joints. 
The prothorax has the pronotum flat, the sides coarsely and irregularly crenulate 
so that it would be incorrect to say that there either is or is not a lateral margin. | 
The prosternum is rather large, the length of the band in front of the coxa being 
equal to that of the coxal cavity, along the middle in the longitudinal direction it is 
flat, and shows no trace of any thickening along the middle, it is prolonged back- 
wards between the rather widely separated coxze, so as to form a flat, short, broad, 
prosternal process, the extremity of which is truncate-rounded : the side pieces are 
large, the suture between the anterior and posterior of them is in some individuals 
difficult to detect, but when seen it is found that the posterior piece is of large area, 
probably more than half that of the anterior piece. The coxe are suborbicular and 
rather small. 
The mesosternum is rather small, and its plane of extension is almost a continua- 
tion of that of the metasternum, so that in the natural condition the mesosternum 
is quite visible between the meta- and pro-sterna, its epimera are triangular: thus 
the general form and relative size and disposition of its parts are singularly similar 
