270 Bashford Dean Memorial Volume 



In all five of our preserved specimens, the tongue (Figures 8 and 9, plate III) does 

 not in any case reach far enough forward to come into apposition with this valve-like 

 structure. But in all of these specimens, on each side between the tongue and the lower 

 jaw, there is a prominent loose fold of tissue which during expiration might come into 

 contact with the crescentic fold, and thus enable the shark to breathe with its mouth 

 partly open. Somewhat similar structures are known to occur in skates and rays. Also, 

 Gudger has found in various teleostean fishes at Tortugas, Florida, similar dorsal breath' 

 ing-valves and similar loose folds of skin alongside the tongue. He has verified the func 

 tion of these structures in Hving fishes. We infer therefore that the structures we have 

 just described in Chlaynydoselachus function exactly like the similar structures present in 

 living fishes. 



At the time the above was written, we believed that we had discovered a structure 

 hitherto unnoticed in Chlamydoselachus. However, our study of an article by AUis 

 (1914), based in part on Chlamydoselachus material supplied by Dean, showed that we 

 had been partially anticipated. In his specimens AUis found across the front part of the 

 roof of the mouth what he describes (p. 354) as 



a nearly horizontal shelf across the anterior portion of the large and deep subethmoidal 

 depression on the ventral surface of the neurocranium. This subethmoidal depression is 

 shown in both Carman's and Goodey's figures, but is not there as pronounced as I find it in 

 all of the several specimens that I have examined. 



Continuing he says: 



The mucous membrane of the mouth cavity lines the walls of the subethmoidal depres' 

 sion and is reflected, first posteriorly and then anteriorly, to clothe first the dorsal and then 

 the ventral surface of the horizontal palatine shelf, a mucous fold with a supporting core of 

 cartilage thus being formed, dorsal to which there is a large and deep suprapalatine recess in 

 the roof of the mouth cavity. When the mouth is opened and shut some slight movement 

 must necessarily be given to this mucous fold, and the overlying recess must be correspond' 

 ingly enlarged or diminished in capacity. 



In the closely related form, Heptanchus, AUis found "a large pocket ... in the roof 

 of the mouth cavity. . . [which] extends but Httle if at all dorso-anterior to the dorso' 

 posterior edge of the palatine process." Returning to Chlamydoselachus, he states: 



The palatine process of Chlamydoselachus does not definitely articulate with the 

 lateral edge of the solum nasi, simply resting against its ventral surface in certain positions of 

 the upper jaw, and probably sUding slightly upon it in a latero-mesial direction. If this 

 sliding contact were to become a definite articulation, such as is to be found in teleosts and 

 bony ganoids, it is evident that that part of the palatine process that lay mesial to the Hiie of 

 contact would be a hindrance to the free articular movements of the parts concerned, and 

 that it would accordingly tend to become detached or resorbed; and if resorbed it would 

 evidently leave a fold in the mucous Lining of the mouth cavity that would strikingly re' 

 semble the maxillary breathing valve of many teleosts. 



Then AUis goes on to say definitely that he believes this structure in Chlamydosel- 

 achus to be the homologue of the maxillary breathing'valve found in teleosts. We have 



