1909.] OLFACTORY ORGAN OP TELEOSTEAN FISHES. 645 



and Mullus and Pagellas on the other, in which the posterior 

 nostril is valved and the sacs open into a definite part o£|the 

 olfactory chamber by restricted orifices. 



A parallel specialization is also observable in the difierentiation 

 of the jaw-muscles in these two groups. 



SCOMBRIFORMES. 

 SCOMBRID^. 



Scomber scomhrus. 



The nostrils lie in the posterior half of the distance from the 

 eye to the snout separated by a bridge of skin 8 mm. or so in 

 breadth. The anterior nostril is a small and quite simple circular 

 hole, the posterior a vertical slit about 4 mm. long, and valved 

 against ingress by the thinness and flexibility of its backwardly 

 directed anterior lip. 



The olfactory rosette is prominent and sharply defined, and 

 lies as usual directly beneath the anterior nostril. It consists of 

 about 30 claw-shaped laminte arranged as usual radially around 

 the hinder parts of a linear raphe. 



The olfactory chamber is dilated posteriorly and below to form 

 an extensive though veiy shallow accessory sac, which is divided 

 into upper and lower parts by the ethmo-lachrymal articulation, 

 the upper part passing beyond the posterior nostril to the anterior 

 and upper edge of the orbit, the lower extending downwards and 

 forwards upon the palatine bone and buccal membrane to the 

 upper border of the maxilla, b}^ which it is comjjressed when the 

 mouth is closed. 



Zeorhombi. 



Zeid.e. 

 Zeus faher. 



The nostrils lie close in front of the eye, near the dorsal mid- 

 line of the face. Both are wide open and of large size, the 

 anterior being a circular aperture about 3 mm. in diameter, with 

 a thick but low tubular lip higher behind than in front, and the 

 posterior a large bean-shaped opening (7 mm. x 4 mm.) lying- 

 close behind the anterior, and partly embracing it with its concave 

 border. 



The rosette, which is plainly visible through the posterior 

 nostril, is prominent and sharply defined. It consists of a 



Explanation of Text fig. 209 (see opposite). 



Paffellus centrodontus. 



A. Olfactory organ in position, from the side. 



B. The same, from above. 



C. The valve (V) upon the hinder lip of the posterior nostril, in section. 



D. Diagranr of a lamina of the rosette. 



BM., bnccal membrane. R.PMX., retractor premaxilla. 



