Mr. G. W. Kirkaldy on Aquatic Rhynchota. 57 
Ventral surface entirely black, except the connexivum, which 
is sordid testaceous, the junctures of the segments narrowly 
black. 
Long. 16-16°7 millim. ; lat. pronot. 6 millim. 
Ngan Hoei, Ho-Chan (China): Montandon’s collection 
and mine (kindly presented by Prof. Montandon). N. China: 
British Museum. 
The species of the family Notonectide are exceedingly 
difficult to diagnose satisfactorily separately ; the structural 
characters are very obscure and not always constant ; more- 
over, such characters as the punctuation of the head and 
pronotum (which, in conjunction with others, are used so 
extensively in other families of the Rhynchota) appear to be 
quite valueless here. The coloration of the hemielytra as a 
diagnostic character is here not only valueless, but even 
misleading. Almost the only satisfactory method left is the 
comparative, and that ceases to be satisfactory when one does 
not possess the other species necessary for comparison ! 
Montandoni is structurally very close to both tréguttata 
and chinensis; the hemielytra of the two latter, however, 
appear to be somewhat laterally sinuate and slightly dilated 
at the lateral margins of the corium, about one third of its 
length from its own apex ; there is not the slightest trace of 
this in Montandont. 
In chinensis the head is very much narrower towards the 
base ; from the base the lateral interior margins of the eyes 
keep almost parallel for a little space, then diverge (but not 
much) ; the vertex in this species is more than three times as 
wide as the narrowest part of the head (close to the base) ; in 
triguttata the head is wider basally than in chinensis and is 
not so widely divergent, the above-mentioned margins of the 
eyes are sensibly curved, and the vertex is a trifle more than 
two and a half times as wide as the narrowest part of the 
head; in Montandoni the head is wider both at the vertex 
and base, and the interior margins of the eyes are much 
straighter. 
From the above notes it may perhaps appear that Mon- 
tandoni is intermediate between tréguttata and chinensis ; 
but, from an exhaustive examination of a number of specimens 
of all three species, I am convinced that such is not the case ; 
although Montandont and chinensis are so similar in colour, 
it is rather triguttata that is the intermediate species. 
I have much pleasure in dedicating this large and hand- 
some species to my learned colleague Professor Montandon, 
who has helped in such a great degree, from his wide expe- 
rience and extensive labours, to increase our knowledge of 
