1909.] 



OLFACTOKY ORGAN OP TELEOSTEAN FISHES. 



623 



deflected, during the forward progression of the fish, through the 

 anterior nostril down amongst the laminje of the rosette. 



Text-fig. 195. 



B 



A. Diagram of nostrils and olfactory chamber of Tinea vulgaris in 



longitudinal section. 



B. A similar diagram of the olfactory organ of Ahramis hrama. 



The olfactory chamber occupies the usual position with regard 

 to the bones of the face, and lodges a rosette of 30 or so laminje 

 radiating in the usual way from a linear raphe. The linguiform 

 pi'ocess upon the free border of each lamina is peculiarly long and 

 narrow, especially in the hinder parts of the rosette where they 

 form a tuft projecting freely into the posterior nostril. 



An essentially similar condition of the olfactory organ was 

 found in Misgitrnus fossilis and in Laheo zoneus. 



Ahramis hrama (text-fig. 195, B). 



In this genus also the olfactory organ is essentially similar to 

 that of Tinea with, however, the rather important absence of a 

 hood-like extension of the posterior lip of the anterior nostril. 



SiLURIDJE. 



Clarias lazera (text-fig. 196, p. 624). 



The nostrils lie upon the dorsal surface of the face, the anterior 

 at the end of a short tube overhanging the upper lip, the j^osterior 

 at some distance (about twice the diameter of the eye) further 

 back. The upper and under margins of the posterior nostril are 

 produced to form thin membranous lips, that would act as valves 

 to prevent inflow of water by this nostril to the olfactory cavity. 

 At its anterior corner is a long nasal tentacle. 



The olfactory cavity extends from nosti-il to nostril but is 

 separable into two distinct segments — (1) an oval chamber in 

 which lies the olfactoiy rosette, with its long axis directed from 

 the anterior nostril backwax'ds and to the mid-line, and (2) a 



