no E. EAMSAT "WEIGHT ON THE SKULL AND AUDITOEY 



having shown the existence of a reduced Weberian apparatus in the Hypostomina, Sage- 

 mehl concludes that Arges and Brontes, the uuarmoured relatives of this group, must 

 likewise possess one. Day has demonstrated the existence of an air-bladder surrounded 

 by bone in Bagarius and Glyptosternum ; Sagemehl, a similar condition in Trichomycteres 

 (which is a near relative of Eremophilus), so only Cetopsis and Hj'pophthalmus remain, 

 but these, after experience with the other genera, evidently rec[uire a thorough revision 

 before one can confidently assert the absence of Weberian apparatus. 



The present paper is intended to furnish the necessary revision for Hypophthalmus, 

 which, it will be shown, does not depart from the ordinary Siluroid type in this impor- 

 tant respect. 



If the skull of Amiurus be macerated, the first vertebral centrum separates readily 

 from the basioccipital, and the neural spine which projects forwards from the region of 

 the third vertebra and articulates with the exoccipitals and supraoccipital spine, likewise 

 comes away with ease. The union of the conjoined anterior vertebrœ with the skull in the 

 only Hypostome I have examined [Lijmsairns pardalis) is more intimate, but by no means 

 so much so as to prevent the separation of the parts by maceration, and the study of the 

 ossifie centres of the hinder region of the cranium (cf. Grôldi, No. 3, p. 414.) But Hypoph- 

 thalmus conducts itself differently in this respect, complete ankylosis of the conjoined 

 anterior vertebra; with the skull taking place, first, between the centra- and the basi-occi- 

 pital (Fig. 2), secondly, between the roof of the neural canal and the supra- and ex-occi- 

 pitals (by means of perichondral bone which does not, however, obliterate the cartilaginous 

 boundaries of the foramen magnum from the internal aspect), and thirdly (indirectly) by 

 means of the supraclavicles, which are fused with the anterior expanded ends of the fourth 

 transverse processes, and with the neighbouring pterotic and epiotic regions of the skull 

 (behind /e in Fig. 3.) In Figs. 1 and 2, which represent the cranium from the dorsal and 

 ventral aspects respectively, the anterior conjoined vertebrœ are represented in their 

 natural connection with the skiall, the sixth, seventh, and eighth (free) vertebrae being 

 also included, to indicate the contrast between these and the conjoined vertebrœ. The 

 posterior limit of the skull bounded by the supraoccipital and epiotics is sufficiently dis- 

 tinct on the dorsal aspect, much less so on the ventral where the supraclavicles, sending 

 their medial processes towards the basioccipital, tend to conceal the hinder wall of the 

 skull. As observed above, complete osseous union takes place between the supraoccipital 

 spine and the neural spines of the conjoined vertebrœ. The supraoccipital spine itself is 

 deeply grooved on its dorsal aspect as far forwards as the cranial fontanelle. A ridge is 

 readily observed continuing the epiotico-pterotic suture on to the dorsal surface of the 

 supraoccipital, and marking olf an anterior part on each side, sculptured like the frontals, 

 and a posterior part which serves for the attachment of part of the dorsal musculature. 

 The former correspond to the parietals which in the Nematognathi are confluent with the 

 supraoccipital (Cope, No. 1, p. 330.) From the figures it will be observed that the com- 

 plex supraoccipital articulates with the exoccipitals, epiotics, pterotics, sphenotics, and 

 frontals. Only a partial study of the other bones of the occipital segment can be made 

 from Fig. 2. As in all the Nematognathi I have examined, the basioccipital articulates 

 with processes of the supraclaA'icles, which in this case project obliquely forwards towards 

 it, while their direction in other cases is transverse. Eight and left of the basioccipital 

 appear the exoccipitals, the form of which will be gathered more readily from the sections 



