428 Edward Phelps Allis jr., 



organ of the line should be the postfrontal organ, the 7 th. pore being, 

 like the 6 th. pore in Auchenaspis, the double pore formed primarily 

 where the main infraorbital and supraorbital canals anastomose. 

 Beyond this 7 th. pore the canal is said to lie in the so-called post- 

 frontal bone, and as nothing is said as to the 7th. organ lying in 

 that bone, it is practically certain that that organ lies at the extreme 

 anterior edge of the squamosal, and that the so-called postfrontal is, 

 as in Ameiurus and Silurus, a sphenotic (postorbital ossification) and 

 not a postfrontal. On leaving this sphenotic bone, the canal enters 

 the squamosal, which bone probably lodges the 7th., 8th. and 9th. 

 organs of the line, organ No. 9 evidently being an extrascapular organ. 



The preopercular canal of this fish, after it leaves the lower end 

 of the preoperculum, passes, according to Pollard, "into the dermis 

 and branches dichotomously, one branch, the anterior, opening shortly 

 at pore 1 and not continuing on into the lower jaw while the other 

 branch, really a continuation of the canal, runs backward and down- 

 ward in the interoperculum showing in that bone the sense organ 

 marked 1 in fig. 6". This apparent irregularity in the course of this 

 canal has been quoted as evidence that latero-sensory organs may be 

 found on the gill-cover of teleosts, and that as they are here, in 

 Chaetostomus, enclosed in the latero-sensory canals, they must be of 

 the same category as the organs of the pit lines of Amia. But, 

 assuming that the observation is correct, the apparently aberrant 

 course of the canal must certainly be capable of some explanation 

 that would involve the introduction of mechanical causes only, and 

 not that of sense organs other than those belonging to the regular 

 preopercular line. 



Clarias. In an adult Clarias, Pollard [60] finds six sense organs 

 in the supraorbital canal. The canal first traverses the nasal bone, 

 that bone lodging two sense organs of the line. It then traverses a 

 bone called by both Pollard and Huxley [48] the prefrontal, but this 

 bone lodges no sense organ of the line. It is therefore not a latero- 

 sensory ossicle, and although said to be traversed by the supraorbital 

 canal, and said by Pollard to be a dermal bone, it would seem as if 

 it must be the homologue of the antorbital ossification (lateral eth- 



