Mr. G. A. Boulenger on a new Species of Mormyrus. 193 
We may sum up our results as follows : — In the Schizo- 
pods and in the abranchiate larvae of Decapod Crustacea 
respiration is purely cutaneous and is principally effected in 
the membrane which clothes the lateral walls of the carapace. 
In the adult Decapods this respiratory apparatus persists, and 
presents an absolute fixity, at any rate as far as regards its 
large efferent canal ; but a secondary respiratory system is 
added to that of the larva, and it is this latter system, in 
which the branchiae are intercalated, which is really the only 
one described in the classic works. This branchial system is 
undoubtedly the more important from a physiological point 
of view (except perhaps in the terrestrial species) ; but it is 
a secondary apparatus which in no way lessens the import- 
ance of the cutaneous system. 
XX Y. — Description of a new Species of Mormyrus. 
By G. A. Boulenger. 
Mormyrus mento. 
D. 29. A. 36. Y. 6. L. lat. 85. L. tr. If. 
Snout short, curved, once and a half the diameter of the 
eye, fV the length of the head. Mouth terminal, on a line 
with the lower border of the eye, its width one fifth 
the length of the head. Teeth moderately large, notched, 
five in the upper jaw, six in the lower. Diameter of the 
eye one fifth its length, about two thirds the width of the inter- 
orbital space. Chin strongly swollen. Origin of the dorsal 
halfway between the gill-opening and the caudal, and above 
the ninth ray of the anal. Pectoral as long as its distance 
from the nostrils, extending a little beyond the base of the 
ventral, which measures nearly half the length of the head. 
Depth of body 3^ times in total length (without caudal), 
length of caudal peduncle 5J times ; depth of caudal peduncle 
one fourth its length. 12 scales round the caudal peduncle. 
Silvery, with fine brown dots, which are very crowded on the 
head and the dorsal and ventral lines. 
Total length 190 millim. 
Closely allied to M. senegalensis , Stdr., from which it is 
distinguished by the smaller scales and the more slender 
caudal peduncle, and to M . cyprinoides , L., which has smaller 
teeth and a deeper caudal peduncle surrounded by 16 scales. 
A single specimen, from the Gaboon. 
