WEALDEN FORMATIONS. 11 



The premaxillary teeth are five in number in each bone; the three middle ones 

 subequal, the first and fifth smallei. The maxillary teeth are divisible into laniaries and 

 carnassials or trenchant molars. The first maxillary tooth is small (PI. Ill, fig. 5) ; 

 the second and third gain quickly in size, the latter (a) assuming the character of a 

 canine ; the fourth tooth (b) is a still larger canine ; the fifth (c) and sixth (d) decrease in 

 size somewhat suddenly, but in length rather than breadth of crown, and terminate 

 the series projecting from the convex part of the alveolar border of the maxillary. The 

 tooth c or d may be said to terminate the laniary series. Beyond d the teeth lose 

 length and slightly gain in breadth ; the crown assumes a triangular, laterally com- 

 pressed, or lamellate form, and the enamel is transversed on the outside by fine but 

 distinct lines (ib., fig. 6, e). Of these sectorial or carnassial molars some of the 

 detached specimens of maxillary (figs, 7 and II) indicate as many as eight or nine. 

 The broad base or root of each tooth is not inserted into a separate and complete 

 socket, but is lodged in a recess of the outer alveolar wall ; moreover, the partitions 

 between these recesses are low or partial, and the teeth appear to have been applied 

 thereto, without being so completely confluent therewith, as in the pleurodont mode of 

 fixation of the teeth in certain Lizards. Hence, in some of the specimens of the 

 maxillary bone the incisors and canines only arc retained, being rooted each in its own 

 complete socket ; while the molars have fallen out, and their partially separated recesses 

 are shown, as in figures 7 and II. 



In the lower jaw the foremost tooth is rather larger than those which interlock 

 with the middle premaxillary or ' incisor ' teeth above ; but not any of the succeeding 

 laniary teeth attain the size of the upper canines. The twelfth tooth, counting back- 

 wards, assumes the lamellate, triangular shape of striate crown characteristic of the 

 superior sectorials ; and the inferior ones wero lodged, like those above, in a common 

 depression of an outer alveolar wall, developing the ridges dividing such depression into 

 the dental recesses, as shown in fig. 16, PI. III. This approximation to a Lacertian dental 

 character might seem ground for something more than a family section of the order 

 Crocodilia; but the quasi-pleurodont attachment of the hinder teeth in Theriosuchus 

 is only an extension of the character affecting some of the teeth in existing species of 

 Crocodile.^ 



In the cranial platform of TJieriosucJms the medial parietal part of the hind border is 

 less convex and the two outer parts are more concave by reason of the further backward 

 production of the mastoids than in Nannosuchus. The lateral borders of the sculptured 

 part of the platform are more convex than in that genus. This is owing to the greater 

 proportion of the outer and posterior angles of the platform which is abruptly depressed 



^ It is noted in the Alligator niger. "No. 765. The right ramus of the lower jaw, from which 

 the posterior part of the inner alveolar wall has been removed, showing the five posterior teeth lodged in a 

 common alveolar groove." ' Osteological Catalogue, Museum of the Royal College of Surgeons,' 4to, 

 vol. i, p. 1G7 (1853). 



