Genus LHydalicus. 217 
us, by reason of the post-medial irroration being less heavy aud 
more sparingly distributed, these transverse bars are more clearly 
defined and obvious; in form they seem to agree the one with 
the other (the anterior margin is more or less suffused, and hence 
indistinct, while the posterior is more marked and more sharply 
defined; this posterior margin is obliquely transverse and wavy 
in outline, tending somewhat towards the apex as it approaches 
the suture ; the suture also between the transverse bars is narrowly 
black); the position, however, of the medial band differs from 
that in HZ. sobrinus, being medial rather than post-medial. 
I am indebted to my good friend Mr. Ussher, of the Com- 
missariat, for a fine series of this species, which he took at Cape 
Coast Castle, in West Africa. Upwards of 100 specimens are 
before me, which present no variety in form or degree of 
coloration. They all appeared suddenly after rains, in a locality 
where there had been previously no water at all, and where a 
short time after all traces of water entirely disappeared. 
12. H. Leander, Rossi (Fn. Etrusce. i. 212). 
A species found in the south of Europe; and also, as it would 
seem, throughout the whole of Africa. Lucas reports it as found 
in Algeria, Aubé in Senegal, Boheman in Caffraria. In 1860 I 
received a series of a Hydaticus from Mr. Cuming from the 
White Nile, which I cannot but refer to this species: the question 
however is not without difficulty, for certainly there is a clearly- 
marked difference between my White Nile examples and the Caf- 
frarian type which I have received from M. Boheman, as well as 
the ordinary European form. The examples before me are con- 
siderably shorter and relatively broader than the South African, 
and a trifle shorter as well as much paler than the ordinary Eu- 
ropean exponents: the basal marking of the thorax, referred 
to in Aubé’s description and present in all other examples that 
have come before me, is absent in the White Nile specimens. 
I have not however sufficient evidence before me to warrant the 
erection of them into a separate species. 
13. H. grammicus, Sturm (Germ. Fn, xiii. 1), 
I am unable to separate from this well-known European species 
certain examples of the genus which were taken by Mr. Adams 
near the coast of China, and by Mr. Wallace in the Eastern 
Archipelago. The insect would seem hence to have not only a 
broad but a very unusual range. It is reported by Aubé as also 
found in Armenia. 
