150 BR. OWEN ON THE PURBECK 
their dentition, generic distinction from both Goniopholis* and 
Petrosuchus. . 
The number of maxillary and mandibular specimens, of which 
three are figured in Pl. IX. figs. 4, 5 and 7, exemplified a degree of 
constancy in size which begat a conviction that such was a character 
of the species; and, diminutive as were the Reptilia in question, 
their characters were indisputably those of the order Crocodilia. 
One of them, by the size and shape of certain teeth, came nearer to 
Gontopholis; another, by the same characters, resembled Petrosuchus ; 
but the differences were such as could not have been obliterated by 
growth or age. 
Theriosuchus approaches, like Goniopholis, nearer to the type of 
the broad-faced Alligators in the proportion of the antorbital part 
of the skull (fig. 1, 0, n) ; but the dentition is more modified than 
in any other known Crocodile, recent or extinct, and approaches 
nearer to that which characterizes the Theriodont order of Triassic 
Reptilia t. 
The premaxillary teeth, five in number in each bone, are small ; 
the three middle ones subequal, the first and fifth smaller; the 
maxillary teeth are divisible into laniaries (fig. 3, 7) and carnassials 
or trenchant molars (ib. m). The first maxillary tooth is small, 
the second and third gain quickly in size, the latter (fig. 5, a) 
assuming the character of a canine; the fourth tooth (ib. 6, and fig. 6,b) 
is a still larger canine; the fifth (fig. 6, 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 ¢ 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 
compressed or lamellate form, and the enamel is traversed, on the 
outside, by fine but distinct lines (fig. 6, ¢). 
Of these sectorial or carnassial molars, some of the detached 
specimens of maxillary bones (figs. 4 and 5) indicate as many as 
eight or nine. The broad base or root of each tooth is not inserted 
into a separate 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 im certain lizards§. Hence in some of the 
specimens of the maxillary bone the incisors and canines only are 
retained, being rooted each in its own complete socket, while the 
molars have fallen out, and their partially separated recesses are 
shown as in the figures cited. 
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 
* * Monograph of Purbeck Reptilia,’ Pal. vol. 4to, 1878, pls. i-iv. 
+ Ib. ib. p. 10, pl. vi. 
{ Quart. Journ. Geol. Soc. 1876, vol. xxxii. p. 99. 
§ See ‘ Odontograpby,’ p. 266, 
