26 



MR. K. LEONARD GILL OX THE PERMIAN 



a label in his writing with the word " teeth.'*' As a matter of 

 fact, a considerable pi-opoi-tion of all the specimens exhibit teeth 

 or some trace of teeth when they are exanjined with sufficient 

 magnification a,nd suitable lighting. Text-figs. 5 and 6 taken 

 together show the dentition fairly completely. Long styliform 

 teeth are borne by the premaxilla, the narrow shaft of the 

 maxilla, and the anterior half of the dentary. The foremost 

 teeth on the dentary are especially long and curved, and it is 

 these that are most frequently found preserved. A single speci- 

 men suggests, though not conclusively, that there were minute 

 teeth on the splenial. The vomer is bordered by short, very 



Text-fiffure 5. 



rpo. 



Ipmx 



Acentrojohoriis varians. Head showing dentition; Kirkby Collection, Hancock 

 Museum. About four times natural size, an., angular ; cor., circumorbital ; 

 dn., dentary ; 7tm., hyomandibular (part) ; i.op., interoperculum (space left by 

 it) ; l.;po., left preoperculum ; l.pmx., left premaxilla ; l.sy., left sj'mplectic ; 

 mx., maxilla ; op., operculum ; r.j., right ramus of lower jaw ; r.j.s., 

 probablj- right splenial, displaced ; r.pmx., right premaxilla ; r.po., right 

 preoperculum ; r.si/., right symplectic ; sa., coronoid (supra-angular) ; s.op., 

 suboperculum ; vf., vomerine teeth ; x., possibly the right ceratohyal. 



stout teeth ; they usually have the appearance of rounded knobs, 

 but the best examples show them to have had short conical 

 points. In one specimen that seems to show the buccal surface 

 of the vomers, there is a suggestion of inner rows of stud-like 

 tritoral teeth, but they are too obscure to warrant a positive 

 statement. A few specimens, notably the one from the Sunder- 

 land Museum represented in text-fig. 6, show that the palato- 

 pterygoid also bore small conical teeth. 



The opercular apparatus is remarkable in the same way as the 

 jaws, namely in that it is so typically of- the Semionotid pattern. 

 Text-fig. 6 and the restorations make its composition clear 



