PURBECK CROCODILES. C51 



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 11) 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 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 figures 7 and 11. 



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

 with the ttiiddle 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 wer& 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. 44. This approximation to a Lacertian dental 

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

 Crocodilia ; but the quasi-})leurodont attachment of the hinder teeth in Theriostichus 

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

 Crocodile.^ 



In the cranial platform of Theriosuchus 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 

 below the level of the sculptured surface of the mastoid, and which becomes smooth like 

 the contiguous and lower-placed tympanic. This character, shown in the subject of 

 fig. 3, PL 44, usefully indicated fragmentary parts of the skull of other individuals of the 

 species, such as are figured in fig. 1, 12', PI. 45. The supra-temporal vacuities are relatively 

 larger than in Naimosuchus. The intervening tract of the parietal, rather more canaliculate 

 than in Nannosuchus, is divided by a mid ridge in two of the cranial specimens, and 

 partially so in the more complete skull. 



No palpebral ossicle is preserved in the orbit (o). The pointed ends of the nasals are 

 produced so as to divide the outer nostril into two, as in some specimens of Crocodilus 



' It is noted in the Alligator niyer. "No. 7G5. 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 Eoyal College of Surgeons,' 4to, 

 vol. i, p. IC; (1853). 



