354 Pi'of. Owen's Descrijif'Kj» of the Lepidosiren annectens. 



M. Agassiz has confirmed this statement, and further observes, that the 

 ductus pneuniaticus comuiunicates with the pharynx by a large and regular 

 slit, which he regards " as bearing even a closer resemblance to the entrance 

 of the trachea of the Pulmoniferous Vertebrata in general, than the aperture 

 by means of whicii the lungs communicate with the pharynx in the Perenni- 

 branchiate Amphibia*^ In tlie Poh/pferus, lastly, we find an approach to 

 the Lepidosiren in the air-bladder being double, consisting of two long cylin- 

 drical lobes, but of unequal length, the left being the longest, and extending 

 through the whole length of the abdomen : the communication of the trachea, 

 or ductus pneuniaticus, with the oesophagus, is also here described by Geoffroy 

 St. Hilaire as consisting of a fissure provided with a constrictor muscle. 



The Poh/pfents, moreover, presents a most interesting trait of affinity to the 

 Lepidosiren in the shortness and straiglitness of its intestinal canal, which is 

 provided with an internal spiral valve. 



With these advances in the organization of the air-bladder in certain abdo- 

 minal Fishes towards the reptilian structure of the lung, made by the Atniu 

 and LepidosteKs on the one part, in the cellular complication of a single cylin- 

 drical air-blatlder ; and by the Poli/pterus, on the otiier hand, in the division 

 of the air-bladder into two lobes, with the slit-shaped glottis of the ductus 

 pneuraaticus described by Geoffroy anti Agassiz ; there wanted only the com- 

 bination of the tiiree characters, as it occurs in the Lepidosiren, of a double 

 as well as cellular air-bladder, with a rudimental larynx, to dissipate the last 

 doubts entertained by the stanchest realist as to the true homology, long ago 

 pointed out by Ilarveyand Hunter, of the vesica natatoria and ductus pneu- 

 niaticus of the ichthyologist. 



Having indicated some of the affinities of the Lepidosiren, considered as a 

 Fish, to certain species of the Sauroid family, I may further observe, that in 

 the helmet-like plate into whicii a part of the frontal is developed, we perceive 

 a resemblance to the genus Heterobranckus amongst the Siluroid family of 

 abdominal soft-finned Fishes, most of the species of which also possess a 

 bilobed air-bladder communicating with the oesophagus, and are deficient in 

 pancreatic cseca. 



When we consider also tliat the Esoeidce have all a large air-bladder, and 



* Zoological Proceedings, 1834, p. 119. 



