14 (^A,LIK(li;.\'lA ACADK.M Y OK SCI K.NCKS 



lu)wevov, very pronounced and must have carricil the vomerine teetli down to 

 meet tlie low posterior teeth of the mandihulai' series. 



Tlie foi'm of the pi'evomer seen here suii'iicsts tlie Khynehoeephalia, hut 

 differs fi'om the known types in tlie character of the (h'utition. The hi'oa(h'ned 

 teeth of the posterior portion of the hone liad possil)ly a function somewhat 

 simihir to that of the smaHer vomerine teeth of the Choristodera; hut they were 

 much less numerous, were much larger, and were confined to the lateral margins 

 of the palatal surface. 



The inferior narial openings in ThalaUosanrtis are large and are situated 

 almost immediately l)elow the superior openings, the anterior horders being 

 slightly anterior to the posterior borders of the upper openings. The external 

 borders are formed in part hy the ma.xillaries, as the anterior ends of the j)alatines 

 d(j not appear to come in contact with the ])revonier here in the manner in 

 which they do in the ('horistodera. 



The anterior ends of the palatirt.es are turned upward i)ehind the nai'ial 

 openings and art' deeply grooved to form the posterior walls of the nasal pas- 

 sages. As seen in section a (IM. ii, lig. la) the external hoi'dcr of the palatine is 

 enfolded by the thin posterior end of the maxillary. In 7'. pcrriiii (IM. iv, tig. '.\) 

 the same relations are seen, only tlie narial opening is smaller. The median 

 border of the palatine swings far around the nares here as if it had probably 

 joined the prevomer hi'oa<lly. The relations of the posterior and median sides 

 of the palatine are only imperfectly known. The groove on the median si<le of 

 the element (PI. iv, tig. ;>) is not such a contact as Avould occiu' if the correspond- 

 ing element from the other side were met here. The presumption is that the 

 anterior end of the pterygoid passing along the median l^ordi-r of the palatine 

 was in contact with this surface. 



In none of the skulls examined have there l)een found any indications of 

 the existence of teeth on the palatine. In two specimens (PI. in, fig. ."! and 

 PI. IV, fig. 3) this element can be seen in place and has been followed backward 

 for a considerable distance without showing any traces of teeth, though they are 

 well shown on other elements. The teeth shown close to the palatine on Plate iv, 

 figure •"> are entirely distinct from it. They prol)al)ly belonged to the ptervgoiil. 



One of the most remarkable features of the type specimen of ThalaftomiirKs 

 is a peculiar dentigerous bone which lay below the palatine region and above 

 the separated rami of the mandible, ('onsidering the position of the specimen. 

 the character of the material, and the fact that no bones of other animals have 

 been found in the matrix, there can he no reasonal)le doubt that it belongs to 

 this skull. 'Hiis hone (JM. v, iigs. Ir;, ll> and Ic) is held to he the pteryf/oid. It 

 consists of a narrow, thick plate, one border of which boi'e five rows of teeth. The 



