118 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
well-marked oblique ridge on the ventral surface of its root, and, in the larger of our 
two specimens was greatly thickened in addition to having its posterior margin 
traversed by a deep groove for the insertion of the fibres of the dorsal wall of the 
anterior chamber. 
Excluding Auclienoglanis, Platystoma is a fairly representative type of the more 
normal Pimelodinte, and for this reason a detailed account of the structure and 
relations of its air-bladder has been given. From this point of view the more note- 
worthy features in Platystoma are : — 
(a.) The laxity of the articulation of the anterior vertebrae with the skull through 
the absence of accessory articular or subvertebral processes. 
(6.) The presence of two pairs of extrinsic compressor and tensor tripodis muscles 
in connection with the air-bladder. 
(c.) The absence of any definitely recognisable transverse membrane distinct from 
the skeletally attached outer strata of the lateral portions of the anterior wall of the 
l)ladder. 
(d.) The tendency of the air-bladder to develope antero-lateral caecal appendages. 
In the extensive development of the superficial ossifications, and in the extent and 
character of the skeletal attachments of the anterior wall, as well as in some other 
minor features, Platy'itoma closely resembles the Arioid type, to which reference will 
subsequently be made. 
Platystoma fasciatmn and P. coruscans. 
Johannes Muller (28,* Plate 4, figs. 8, 9) has noted the presence of antero- 
lateral caecal appendages in P. fasciatum similar to those of P. tigrinum, but in 
P. coruscams, if we rightly interpret his brief description of this Siluroid, such 
appendages are entirely wanting. The anterior vertebrae of P. fasciatum have been 
figured and described by Sorensen (37, Plate 2, figs. 13, 14) from whose account 
it would seem that they do not in any important respect differ from those of 
P. tigrinum. 
Sorubim lima. 
Under the name of Platystoma lima, Johannes Muller {loc. cit.) briefly refers to 
this Siluroid as not possessing the caecal appendages so characteristic of the anterior 
chamber of the air-bladder in P. tigrinum and P. fasciatum. 
Piramutana piramuta. 
The anterior vertebrae and their modified transverse processes in this species are 
very similar to the corresponding structures in Platystoma. As in the latter genus 
* See section entitled “ Zellige Schwimmblasen bei einigen Siluroiden.” 
