118 The Rev. W. D. Conybeare's Additional Notices 



1. The maxillary bones (hb) are close togethefj so as to form a solid roof to 

 the mouth. 



2. The palatal bones (e e) and internal pterygoids {//) are likewise close to 

 each other^ so as to form a floor below tlie nasal canal, and thus throw its pos- 

 terior opening far back. 



A greater solidity is thus given to the whole appearance of this part, and 

 the position of the posterior opening of the nasal canal must affect the func- 

 tions of respiration. 



1 cannot discover in this specimen traces of the external pterygoids ; w hich 

 were figured in my former paper on the authority of a specimen that was rather 

 dislocated, and might have exhibited deceptive appearances. It now appears, 

 that the narrow form which that specimen assigned to the palatal bones, 

 must have arisen from its presenting only an impression of them where they 

 project into the nasal canal. 



It would still be desirable, in order to complete our knowledge of the skull 

 of the ichthyosaurus, to procure a series of sections through its posterior part, 

 such as might lay open the internal arrangement of the bones, especially of 

 the sphenoid. Mr. De la Beche, whose local opportunities in examining spe- 

 cimens are great, will keep this object in view, and the result will at some 

 future time be submitted to the Society. 



The notices above given point out all the analogies derived from the oste- 

 ology of the head. To these it is to be added, that the structure of the hu- 

 mero-sternal part bears decidedly a nearer analogy to the lacertae than to the 

 crocodile ; since the clavicular furcula is wanting in the latter genus. 



X. Vertebra. — I have only to add to my former remarks on this part of 

 the skeleton, that the atlas and axis agree exactly with the other vertebrae, as 

 is the case in fish. The statement that these parts appeared to resemble the 

 atlas and axis of the turtle, arose from my having taken a mutilated portion 

 of the occipital condyle, in a dislocated specimen, for the inferior portion of 

 the atlas. 



XI. Extremities. — A more perfect representation of the paddle than has 

 yet appeared is given in PL XX. fig. 1. This will at once show the exact 

 manner in which the series of bones succeed each other. 



PLESIO- 



