1909.] OLFACTORY ORGAN OF TELEOSTEAN FISHES. 651 



Posterior to the rosette, just above the posterior nostril, is a 

 clearly defined oval hole that leads into a two-lobed accessory sac. 

 The lower and larger lobe runs backwards parallel to the margin 

 of the mouth, swelling slightly towards its distal end. The upper 

 lobe lies beneath the upper end of the rosette. These two lobes 

 obviously represent the ethmoidal and lachiymal sacs of more 

 normal genera. 



Upon the blind (left) side, the nostrils are separated by a very 

 considerable distance, due almost entirely to a tubular elongation 

 of the nasal cavity between the rosette and the posterior nostril 

 (cf. Mullus). Both nostrils are tubular, the anterior stout and 

 bluntly conical, the posterior smaller and protected against ingress 

 by the thinness of its converging lip. This nostril opens and 

 shuts with a jerk synchronously with the respiratory movements 

 (Bateson). 



The rosette is similar in form to that of the right side, but lies 

 with its length parallel to the internarial axis. It occupies only 

 the anterior part of the nasal cavity ; behind it a long tubular 

 empty passage leads to the posterior nostril. The lower wall of 

 this passage is dilated between the hinder limit of the rosette 

 and the ethmo-lachiymal articulation to form a long accessory 

 sac, that runs backwards and downwards with the adductor 

 mandibulfe and palatine arcade superficial to it, giving off a small 

 secondary diverticulum forward towards the lower end of the 

 maxilla. 



Summary. 



In considering the Zeorhombi, Zeus can be at once set aside 

 as differing completely from the Pieuronectid^e in all the details 

 of its nose structure. 



The Pleuronectidce examined can be separated into three groups. 



1. Hipjjoglossus and Pleuronectes, in which the laminaj of the 

 rosette are disposed longitudinally. 



2. Rhombiis and Arnoglossus, with a flat, leaf-like lobe to the 

 left anterior nostril. 



3. Solea, with tubular nostrils and elongated Eel-like rosette. 

 In all the genera there are accessory sacs in connection with 



the olfactory chamber, which are comparable to the ethmoidal 

 and lachrymal sacs found in other Acanthopterygians, although 

 they differ in number according to the genus and the side of the 

 face, and except in the Sole are more strongly developed on the 

 ocular than on the blind side. 



Explanation of Text-fig, 212 (see opposite). 



HJiombus maxinius. 



A. Nostrils of the blind (riglit) side. 



B. Olfactoiy oi'gan of the ocular (left) side, in position. 



C. Olfactory organ of the blind side, in position, from above. 



