66 Records of the Indian Museum. [Vor; X Vitae 
certain species in the naked chest and the specialization of the 
muscles of the thorax. In the following key I have made use of 
the first of these characters in my primary division and of the 
second in the first secondary division. It is possible that the two 
primary groups will have to be regarded ultimately as distinct 
genera. 
Key to the Indian and Persian species of Discognathus. 
I. Mental disk small, less than half as broad as head, without a 
specialized posterior border; margins of opercula meeting in 
the middle line well behind the disk. 
A. Disk very imperfectly differentiated, without free pee 
border; barbels 4; chest covered with scales D. adiscus. 
B. Disk with posterior border free but lateral borders not so: 
barbels 4; chest covered with scales D. wanae. 
C. Disk with both lateral and posterior margins ‘free ; 2 bar- 
bels ; the whole of the ventral surface naked D. phryne. 
Il. Disk large, more than half as bread as head, with a free lat- 
eral and posterior granular border, entirely or almost separat- 
ing the opercular margins. 
A. Chest covered with scales, not much flattened ; its muscles 
not highly differentiated. 
tr. Nobarbels. Zid. 44 .. ese . D. imberbis. 
2. 4barbels. J/.1. 36-41. 
a. Pupil of eye in middle or anterior half of head: eye 
usually visible from below; snout tuberculate in male 
but not forming a very distinct process. 
i. Opercular borders approaching one another at an 
obtuse angle on the ventral surface, widely separated 
by mental disk D. lamta. 
. Opercular borders approaching one another closely 
at an acute angle behind the mental disk ; disk sub- 
circular ws, Di potyla: 
b. Pupil of eye distinctly in posterior half of head ; eye 
(except in D. gravelyi) invisible from below. 
. Snout moderately rounded, more or less produced and 
tuberculate, at any rate in adult male, immediately 
in front of or outside nostrils. 
a. Snout forming a single free conical process in front 
of nostrils in all individuals ; opercular borders ap- 
proaching one another at an acute angle on the ven- 
tral surface ; length of head nearly 5 times in total 
length * .. D.stenorhyn- 
g. Snout produced into a pair of conical processes, chus. 
one outside each pair of nostrils a3 . D. bicornu- 
y. Snout produced in male only; its process single, tus. 
usually shorter than in a; opercular margins nearly 
transverse and widely separated on ventral surface ; 
length of head at least 54 times in total Jength ... D. jerdoni. 
. Snout bluntly pointed, never produced in iront of or 
outside nostril ; slightly retroverted at tip. 
a. Dorsal profile from tip of snout to behind dorsal fin 
forming an even rather high curve; depth of body 
5 times in total length . a .. D. gravelyt. 
8. Dorsal profile nearly straight ; that of head sinu- 
ous ; depth of body (in adult) nearly 7 times in 
total length ae. D. elegans. 
. Top of head obliquely flattened ; profile of head and 
anterior part of body a slanting straight line ... D. platyce- 
phalus. 
B. Chest naked, flattened, with specialized muscles. 
