150 THE ENTOMOLOGIST. 



2. Somewhat flat, but elongate ; rostrum short, 

 apparently not jointed ; anterior tarsi more 

 or less spoon- or knife-shaped . . .2. Corixidse. 



2a. Very convex ; rostrum long, with three to four 



segments ; anterior tarsi simple, raptorial . 3. NotonectidsB. 



NAUCORIDiE. 



Of this family, the British species of which are characterised 

 by the somewhat flat broad oval form, we have perhaps three 

 genera, viz. Aplielocheirus, Westwood, Ilyocoris, Stal, and A^aiicoris, 

 Geoffroy ; but the presence of the third is doubtful. 



The following table will separate the three genera : — 



1. Eostrum long, reaching base of mesosternum ; 



head above produced in front of the eyes, 

 and sensibly narrowed, subhorizoutal ; an- 

 tennae reaching a little beyond the sides of 

 the head. Tarsi 2-segmentate, with two long 

 curved claws each ; posterior legs scarcely 

 natatorial. [Always practically apterous.] 

 Figs. 31-34 . . . . 1. Aphelocheiriis, Westw. 



la. Rostrum short, not reaching beyond base of 

 prosternum ; head not produced in front of 

 eyes, but deflected shortly downwards ; 

 antennae thickened, not reaching beyond 

 sides of head. Anterior tarsi unsegmented, 

 destitute of claws ; intermediate and pos- 

 terior tarsi 2-segmentate, with claws ; pos- 

 terior legs natatorial. [Macropterous or 

 brachypterous] ...... 2. 



2. Anterior femora very greatly incrassate ( beneath 



with a small pad of hair near the base), sud- 

 denly ampliated in a right angle at the base 

 beneath, then narrowed. Fjgs. 35-39 3. yaiicoris, Geofifr. 

 2a. Anterior femora greatly incrassate (beneath 

 with broad pad of hair the whole length), not 

 suddenly ampliated beneath in a right angle. 

 Figs. 40-45 2. Ilyocoris, Stal. 



Aphelocheirus* is, in many respects, a link between the 

 Acanthiidae and the Naucorinae, and was indeed placed in the 

 former by its founder. Although the subhorizontal face and 

 long rostrum separate it from the other genera, it clearly belongs 

 to the family. The head above is elongate and horizontal (or 

 nearly so) ; the rostrum long, slender, narrowing towards the 

 apex (fig. 31) ; the antennae consist of four segments, and are 

 apparently destitute of sensory organs, the antennal groove is 

 slight (figs. 32 and 33). The pronotum is deeply excavate 

 anteriorly, greatly expanded laterally, prosternum carinate, 



■•'■ »<}itXv<; (apheles), slender or simple ; ^etp (kheir), a hand. 



