The Latero-Sensory Canals and Related Bones in Fishes. 425 



ma}^ be, it is evident that the parietal of x4.meiurus forms an exception 

 to Boulenger's [IT] statement that, in the Ostariophysi, "The parietal 

 bones either separate the frontals from the supraoccipital or are fused 

 with the latter". 



Silurus glanis. Figs. 8, 9 und 10 show the pores and surface 

 sense organs in Silurus, and also the general course of the latero- 

 sensory canals. 



The supraorbital canal traverses the nasal and frontal bones, 

 and anastomoses, by its penultimate primary tube, with the main 

 infraorbital. 



The line of the supraorbital canal is continued posteriorly by an 

 anterior head line of pit organs, and there is, posterior to this line, 

 a transverse line of similar organs that must be the homologue of 

 the middle head line of Ameiurus. There is an ethmoidal commissure 

 of pit organs, as in Ameiurus, and also other lines, not shown in my 

 sketches of Ameiurus, and which evidently correspond to the vertical 

 and horizontal cheek lines, and the mandibular line of Amia. 



The main infraorbital canal begins in the antorbital bone of 

 Juge's descriptions [52] and on leaving that bone traversed, in the 

 specimen shown in my sketches, four circumorbital ossicles, instead 

 of three as described by Juge. The proximal, or posterior one of 

 these four ossicles was simply a semi-cylindrical scale that supported 

 the infraorbital canal opposite the point of origin of a primary tube 

 that is certainly the double one formed at the point where the infra- 

 orbital and supraorbital canals anastomose. The scale lodged no sense 

 organ, and it is thus unquestionably homologous with the similar ossicle 

 described by Herrick in Ameiurus melas, and to which reference has 

 just above been made. The long ossicle distal to this little scale is 

 thus quite certainly, for the same reasons as in Ameiurus, the dermal 

 postfrontal of the fish. 



Immediately dorsal to the little scale-like ossicle that lies im- 

 mediately dorsal to the postfrontal the main infraorbital canal turns 

 sharply backward, anastomosing at the bend with the penultimate 

 primary tube of the supraorbital canal. It then lies for a short 

 distance in a groove on the dorsal surface of the sphenotic (post- 



