.\IF,i;i;lA.M TIIK. TllALATTiiSAriMA 17 



In T. perriril (V\. iv. tiir. '■'>) the (Iciititiuii df the luwi-r jaw shows ayain the 

 foiiit-al anterior teeth with hiterally eoMii)ressed, low-crowiicd posterior teeth. 

 The depression in tlie hitter is, liowever, very niucii less than in T. alc.randrae. 

 Tn the upper jaw all of the teetli are eouieal. There do not appear to he any 

 low-erowned or laterally compressed maxillary teeth. The most posterior 

 [lortion of the maxillary was apparently I'drutulous ami it is evident that 

 the posterior vomerine teeth were in contact with the posterior portion of 

 the mandihular dentition. 



Jn the type of TltalaftoMtiiriis the perfectly })resi'i-ved ti|) of the crown of an 

 anterior mandihular tooth shows very faint wrinkles in the enamel. ( )n the 

 dej)ressed pcisterior teeth the wrinkling of the enamel is more pronounced and 

 in some instances a faint tul)erculation is visihle. A single loose tooth found 

 with tlie jaws of this specimen has an elongated, somewhat compressed crown 

 covered with numerous strong longitudinal striae. 



Associated with the head hones of T. shafitensis are several loose teetli show- 

 ins the form verv distinctlv. In all of these the crowns are conical, hut thev 

 vary considerahly in length and thickness. The slender, curved teeth (IT. iv, 

 fig. '2h) are prohaldy from the anterior portion of the jaws, and the shorter, 

 heavier ones (Fl. iv, fig. 'Ic) from the middle region. The ci'owns are all sup- 

 ported on heavy fangs, such as are present in teeth inserted in pits. The enamel 

 is marked with numerous tine, longitudinal Avrinkles or striae somewhat finer 

 than those on the corresponding teetli of T. akxandriw. 



In no case has anv evidence been ohtained which would tend to show that 

 the l>ases of the teeth have a foldeil internal sti'ucture as in the Ichthyosauria 

 and (Tioristodera. 



Vomerine Teeth. — In all specimens, so far as is known, v<mierine teeth are 

 present in only two rows, which are set upon the outer edges of the prevomer 

 instead of next the median line. The rows converge anteriorly and near the 

 middle of the prevomer they ai-e very close together. From this point forward 

 they run approximately parallel. In the postt'rior. diverging portions of the 

 rows the crowns are very low and roughly triangulai' in cross-section. In tlie 

 parallel portions the crowns are slightly higher. A \-ei-y sti'iking featui-e of the 

 \'omei'ine dentition is the downward sweep which it takes, the lowest jjoint 

 of the curve being at the place of convergence of the tooth rows. The teeth in 

 this region seem to have come in contact with the low-crowned teeth near the 

 middle of the lower jaw. The [>osterior vomerine teeth e\idently met the pos- 

 terior teeth of the nnindii)le. 



The vomerine teeth are set in depressions and where seen in a cross-section of 

 the j)revomer (Fl. ii, fig. Ic) they ai'e known to extend a considerable distance into 



( 2 j May G, 19«j. 



