HEMIPTERA. 169 
Navcoris, Geoff., Fab. 
™ The labrum in Naucoris is not emarginated, as is the case in the 
following genus, but is exposed, large, triangular, and covers the base 
of the rostrum. The body is almost ovoid and depressed, and the 
head rounded; the eyes are very flat. The antennze are simple, and 
without any projection in the form of a tooth. There is no salient 
appendage at the posterior extremity of the abdomen. The four last 
legs are ciliated, and their tarsi consist of two joints, with two hooks 
at the end of the last. 
N. cimicoides; Nepa cimicoides, L.; Roes., Insect., HI, Cim. 
Aquat., xxxvill. Five or six lines long, and of a greenish brown, 
lighter on the head and thorax; margin of the abdomen serrated 
and projecting beyond the elytra *. 
In the three following subgenera, the labrum is sheathed, and the 
extremity of the abdomen presents two filaments. 
Bexostoma, Lat., 
Where all the tarsi are biarticulated, and the antenne are semi- 
+) 
pectinated }. 
Nepa, Lat.. 
Or Nepa proper, where the anterior tarsi have but one joint, and the 
four posterior ones two, and where the antenne appear forked. The 
rostrum is curved beneath; the cox of the two anterior legs are 
short, and their thighs much wider than their other parts. 
Their body is narrower and more elongated than in the preceding 
subgenera, and almost elliptical. Their abdomen is terminated by 
two sete, which enable them to respire in the oozy and aquatic loca- 
lities at the bottom of which they live. Their eggs resemble the seed 
of a plant of an oval figure, crowned with a tuft of hairs. 
M. Leon Dufour, in the seventh volume of the Animales Géne- 
rales des Sciences Physiques, has published some very curious ob- 
servations on the anatomy of the Ranatra linearis, and of the Nepa 
cinerea. He has discovered in these Insects a peculiar organ, which 
he considers as a kind of pectoral trachea communicating with the 
ordinary trachee. In the first it forms a pair of beautiful tufts of a 
nacre-white, and is composed of numerous ramusculi, which are di- 
rected round a multiplex axis. It is situated inthe midst of the mus- 
cular masses of the pectus. The pectoral tracheze of the Nepa cinerea 
appeared to exhibit the vestiges of a pulmonary ergan. They con- 
sist of two oblong bedies, situated immediately under the region of 
the scutellum, invested by a fine, smooth, satin-white membrane. 
They are almost as long as the pectus, and, except at the two ends, 
free. They are filled with a kind of tow, which, when examined 
under the microscope, presents a homogeneous tissue formed of vas- 
cular arbuseuli. The nervous system appeared to him to consist of 
* Fab., Syst. Ryng.; Lat., Gener. Crust. et Insect., III, p. 146. 
+ Lat., Ib., p. 144; the Nepa grandis, annulata, rustica, Fab. 
VOL. IV. 
