428 PROCEEDINGS OF THE ACADEMY OF [1892. 



crests in the perissodactyls, where they attain such a high develop- 

 ment, arise, as in the molars, from the extension of the intermedi- 

 ate cusps and their coalescence with the internal and external cones. 

 P^ in this species is also tritubercular, but the deutero- and trito* 

 cones are very obscurely marked and the tooth is very much smal- 

 ler than p*. P. primcBvus differs from P. vortmani in the increased 

 size and quadrate shape of P*, and in the much more distinctly sep- 

 arated elements of P^ 



The PeiiptycJitdte have less complex premolars than the preced- 

 ing family. In Periptychus itself the superior premolars, except 

 the first, have deuterocones, which have become crescentoid and 

 thus remotely suggest the corresponding teeth of the true rumi- 

 nants. The composition of the lower premolars is not altogether 

 clear, but p^ and -^ appear to have merely a rudimentary crest-like 

 heel, while p* has a deuteroconid, a rudimentary paraconid and a 

 heel which consists of meta- and tetartoconids. This tooth, there- 

 fore, contains all the molar elements, but still it cannot be called 

 molariform on account of the slight elevation of the heel. Hemi- 

 thlceus has very simple premolars. Fjind^* consist of the proto- and 

 deuterocones only. In the lower jaw the first and second premolars 

 have only the protoconid with no accessory lobes whatever ; the com- 

 position of p' and * is not known. The different species of Anisonchus 

 display an advancing degree of premolar complication. In A. gilUanus 

 P^is a simple massive cone, while P^ and * have well developed deutero- 

 cones. P" has a thick protoconid and very small para- and meta- 

 conids, which are hardly more than elevations of the cingulum. In 

 p* the metaconid is elevated into a considerable heel. The first and 

 second upper premolars of A. sedorius are not known, but in p'^ and ■* 

 the deuterocones have become much enlarged and form crescent- 

 like ridges and minute rudiment? of the tritocone may also be 

 detected. In the lower jaw p^ ^ and * have the para- and metaconids 

 Avell differentiated. In A. corniferus all of the superior premolars 

 are implanted by three fangs, and though it is not certain that p^ 

 possesses a deuterocone, all the others clearly have it. At the same 

 time not even P* has developed a tritocone. The superior premo- 

 lars of Haplocomis are known only for two species, H. lineatus and 

 H. entoconus and both agree in the simplicity of all except P*, which 

 has the usual deuterocone, but in the former species this element 

 forms a crescent, and in the latter a conical tubercle. The lower 

 premolars have metaconid heels of varying degrees of development 



