254 BULLETIN : MUSEUxM OF COMPARATIVE ZOOLOGY. 



Tongue, Plates 12 and 13. 



The tongue of Rhinochimaera is larger than that of either of the other 

 species dissected; it is prominent, free from the floor of the mouth, and is well 

 supported by a forward prolongation of the glossohyal cartilage. At the for- 

 ward extremity it is truncate ; the upper surfaces are covered with papillae, 

 Plate 12. In both of the species of Chimaera dissected the tongue is seen to 

 be much smaller, sharper in front, and to have much less of the glossohyal 

 within it, Plate 13, Figures 1 and 2. The tongue of Callorhynchus callorhyn- 

 chus, Plate 13, Figure 3, is greatly reduced or quite rudimentary, and the 

 glossohyal is not produced into it as in the other forms desci ibed. From the 

 shape of the tongue of Harriotta raleighana, it is evident that the glossohyal 

 is produced into it; the skin of the organ is peculiarly thickened and folded on 

 its upper surface, Plate 5, Figure 5, a consequence probably of rough contact 

 and severe pressure by the hard portions of the food that has established the 

 tritors on the teeth. The tongue of Harriotta is markedly different on the 

 surface from that of either of the other genera, as is sufficiently obvious on 

 comparison with the tongues figured on Plates 12 and 13, all of which are fur- 

 nished with numerous papillae. 



Teeth, Plates 5, 6, 7. 



In all the known recent Chimaeroids the individual possesses three pairs of 

 teeth, vomerines, palatines, and mandibulars, one pair of each ; that is, two 

 pairs of upper and one pair of lower teeth. Some of the fossil forms appear 

 to have had a greater number, and some of the earliest of the extinct tvpes 

 apparently had a single pair of lower opposed to a single jiair of upper teeth. 

 Rhynchodus of the Corniferous and Hamilton limestones, Devonian, descrilted 

 by Newberry from Ohio, is said to be limited to the two pairs, vomerines and 

 mandibulars, so also is Rhamphodus of Jaekel. from the Upper Devonian. 

 These orenera are of some interest in connection with this writino; because their 

 tooth-characters are in certain respects similar to those of Rhinochimaera, 

 which among recent species possesses the most primitive features of dentition. 

 Of living forms the resemblances in the outlines of the teeth are closer thnn in 

 their details of structure. While the differences in these last are excessive, 

 they are so distributed among the genera most closely allied in regard to other 

 peculiarities as to prevent use in distinguishing hiizher groups. This is well 

 illustrated by the teeth of Rhinochimaera and Harriotta, members of a single 

 family, Plate 5, — instances respectively of the least differentiated and the most 

 specialized in dental structures. An abundance of fossil Chimaeroid teeth sug- 

 gests that they may have been shed at times by individuals as in Plagiostomia. 

 "While a periodical shedding of teeth might be expected from what obtains in 

 other forms, we have as yet no evidence of its existence. The worn condition 

 of the teeth in all specimens at hand points rather towar 1 a continuous growth 



