168 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
backwards and pointed at their free distal extremities. Those belonging to the sixth 
vertebra are widely separated from the foregoing, and carry the first pair of 
ribs. As the transverse process of the fourth vertebra contributes nothing to the 
support of the pectoral girdle, the inferior limb of tlie post-temporal (pt.i.) is un- 
usually massive, and articulates internally with an equally stout outgrowth from the 
lateral surface of the basioccipital. For the same reason, and as in Auchenipterus 
and Oxydoras, the ascending process of the same bone has an extensive and intimate 
articulation with the dermal nuchal plates, and with the skull. 
The tripus is normal. The crescentic process (tr.c.) rests upon the flexible root of 
the “elastic-spring” of its side, and describes a somewhat sharp, inward, and down- 
ward curvature along, and in contact with the contiguous lateral surface of the 
complex centrum. The posterior margin of the process is deeply grooved for the 
attachment of the converging fibres of the dorsal wall of the anterior chamber, while 
its ventral surface is traversed by an exceptionally well-marked ventral ridge. The 
depth of the groove and the strength of the ridge suggest that the air-bladder of 
this species is furnished with unusually stout walls. It is not so obvious as in 
Auchenipterus and Oxijdoras that the movements of the tripodes in Synodontis can, 
to any great extent, be limited or controlled by the action of the “ elastic-spring ” 
apparatus. Except that the ascending process is very short the scaphium is normal. 
The intercalarium is a small oblong nodule in the usual position. 
Group : — Ehinoglanina. 
Callomystax gagata. 
In this Indian Siluroid, we again meet with an example of that abnormal type of 
air-bladder in which the organ is longitudinally constricted into two simple lateral 
air-sacs, and more or less completely enclosed within bony capsules formed by the 
modified transverse processes of certain of the anterior vertebrae. But although 
Callomystax bears a general resemblance to such Siluroids as Glyptosternum, Bagarius, 
and others, in these respects it is, nevertheless, not without certain noteworthy 
peculiarities of its own. It is this species that possesses the peculiar modification of 
the confluent spinous processes of the fourth and fifth vertebrm, and the first and 
second interspinous bones of the dorsal fin to form a stridulatiiig mechanism, which 
has already been described by one of us.'"‘ Beyond a brief reference to the air- 
bladder by Day (9), who includes the genus under the name Gagata, in his list 
of those Indian Silurldse, in which the organ is said to be partially or completely 
surrounded by bone, we are not aware of any recorded observations. 
The complex and fifth vertebrae are rigidly connected with each other by the 
* A. C. Haddon, “ On the stridulating apparatus of Callomystax gagata .” — ‘ Journ. Anat. and 
Phj&iol.,’ vol. 15, p. 322 (17a). 
