746 Rey. C. R. N. Burrows on the 
broad. It bears ff. “corona” only on the upper fourth 
of the margin, and is almost covered by spines. The 
“harpe” is without the boot-shaped termination, and is 
attached loosely to the stem of the “clasper.’ Beside 
the “harpe” is a thin semicircular plate of hard chitin 
serrated on its outer edge. This flap is attached loosely 
to the thin chitin of the inner surface of the valve, and 
appears to move readily backwards and forwards. The 
clavus is stout and incurved, very like that of H. nictitans, 
but is accompanied by a quadrate chitinous plate deeply 
serrated on its inner edge. The “cornuti,” about twelve in 
number, are long and thick. 
Thus far our British species. JI am adding two exotic 
forms on account of their interest. 
In H. americana (atlantica) we find the link between the 
last-named species and the other members of the group. 
The “valve” is nearly equal in width throughout its 
length, the “cucullus” being scarcely wider than the rest of 
the valve. The “corona” extends along three parts of the 
margin, and the “cucullus” is very heavily spined along 
the inner margin. The “harpe” is less bifurcate than in 
H. paludis, the “heel” being scarcely developed. The 
“clavus” is short and stout, claw-shaped, with a naked 
point, and is accompanied by a quadrate chitinous plate, 
toothed on its imner edge, and very like the similar 
appendage in H. crinanensis. The “cornuti” are of 
medium size, even in length, and about fourteen in 
number. 
Quite recently I have found amongst a number of 
foreign Hydroecias given to me some time ago by Dr. 
Chapman a male labelled as from Turkestan, which we 
had catalogued after a preliminary examination as being 
HT. crinanensis. More careful examination has proved 
that it does not belong to this species, but to another, 
of which, so far as I know, the genitalia have not been 
examined. This is again practically indistinguishable 
from the other species of the nictitans group. Its peculi- 
arity is that the “valves” narrow off to the “cucullus,” 
which is exceedingly narrow with parallel sides. The 
“harpe” without a foot, is just free from the surface 
of the “valve,” more so than in A. crinanensis. The 
chitinous flap also found in H. crinanensis is very narrow. 
The “clavus” is claw-shaped, strong and thick, and is 
not accompanied by a chitinous plate as in the case of 
