1895.] SEJfSOEY CLNAL SSSTEil OJ? KlSHES. 275 



are described in detail. In all, ttie system is described in four 

 families, viz. the Silurldce, Esoddce, Salmonidce, and Murcenidce, 

 which include eight different species referable to seven genera. 



To Professor T. W. Bridge, M.A., of Mason College, Birming- 

 ham, I wish to offer mj sincere thanks for the specimens of 

 Clarias, CalUchthys, and Pimelodus, and for the very generous and 

 continued assistance which he has given me ; also to Professor 

 W. C. M'Intosh, M.D., F.R.S., for his kindness in granting me 

 the use of a table at the St. Andrews Marine Zoological Labora- 

 ' tory, during the Long Vacation of 1 893. My thanks are also due 

 to Dr. Gi-iinther, F.R.S., who has identified for me the specimens 

 of Pimelodus and Laheo. 



II. SlLUBID^. 



The sensory canal system of certain genera of this family has 

 been previously described by Ramsay Wright (12) and Pollard (11). 

 The former has given a brief account of the canal system in 

 Amiurus cuius and a more detailed account of the cranial nerves. 

 Pollard has described and figured the system and its innervation 

 in Clarias, Galliclithys paleatus, AucJienaspis hiscutatus, Trichomyc- 

 terus tenuis, and Chcetostomiis guairensis. Except in Clarias, he 

 interpreted both the distribution of the sensory canal system and 

 cranial nerves from a series of young specimens cut into sections. 

 Although the cranial nerves of the Siluridce are somewhat difficult 

 to follow, I have preferred dissection as a means of investigation, 

 and it will be noticed on comparing the figures of this author 

 with those here given that there are many points of difference. 



The canal system has been worked out in Clarias nieuhojii, 

 Amiurus catus, Pimelodus maculatus, and Callichihys tittoralis. 

 The cranial nerves in Clarias mar/w, Amiurus catus, and Pimelodus 

 mactdatus. 



1. Clabias NIETJHOni \ 

 General Description, 



The sensory canal system commences as an exceedingly fine 

 canal slightly in front of the base of the caudal fin. As it passes 

 forwards its diameter increases. There are a series of pores 

 opening into the canal, distributed at somewhat regular intervals. 

 The canal traverses the region of the post-temporal and into the 

 squamosal, from which point it may be regarded as the main canal 

 of the head. It gives off a short backwardly directed branch, and 

 immediately in front of this the operculo-mandibular branch arises 

 (PI. XVIII. fig. 1, Ojp.Mn.). From the squamosal the main canal 

 continues along the dorsal border of the sphenotic, and divides into 

 supra- and sub-orbital branches (PL XVIII. fig. 1) : the former 

 passing through the frontal and lateral ethmoid (Parker) and 

 giving off in its course three smaller branches and a commissure in 



^ The specimen upon which all measurements, &c., were made was 360 millim. 

 long. 



18* 



