238 



Bulletin American Museum of N^atural History. [Vol. XXVII, 



and premolars are less differentiated from each other than in the higher 

 types, even the incisors showing an incipient division of the root and a 

 pronounced posterior cingulum cusp. It may however be remarked that 

 these characters of the incisors and canines might perhaps better be regarded 



f>S pa me mts. ^. 



mts 





/;s ''P.% 



mis pS 'P^ >-\,"tts 



' ^,L(e^"i) ^ 



pip 



mts 



Fig. 17. Homology of the molar cusps in the Lipotyphlous Insectivora.- 



No. 1, Dryolestes sp. after Gidley; cingulum after Osborn. No. 2, Microgale dobsoni, original. 

 No. 3, Solenodon paradoxus, original. No. 4, Potamogale velox, original. No. 5, Potamogalc 

 velox, posterior milk molar, after Leche. No. 6, Iclops thonisoni, after Matthew. No. 7, Idops 

 acutidens, after Matthew. No. 8, Gymniira sp., after O-sborn. No. 9, Proscalops miocwnus 

 from photomicrograph (Matthew). 



In the Zalarabdoflonts (nos. 2-5) the para- and metaeones appear to be reduced, the external 

 cingulum gives ri.se to irregular cusps {ps. mts); the high internal cusp according to this 

 view is homologous with the protocone of Dryolestes (no. 1). The basal cingulum in Microgale 

 (No. 2) and Potamogale (nos. 4, 5) grows out into a " pseudoprotocone." 



In the Erinaceoids (nos. 6-8) the simplest molar type (Idops thomsoni, no. 6) agrees in 

 essentials with Dryolestes. The tooth is narrow anteroposteriorly, the paraeone centro-external, 

 the metacone small. The basal cinguhim however (hy) is better developed and confined to the- 

 postero-internal border. In Ictops acutidens (no. 7) the tooth is broader anteroposteriorly, the 

 metacone and hypocone better developed. In Gymnura (no. 8) and Erinaceus the antero- 

 posterior broadening becomes very pronounced and the prominent hypocone completes the 

 quadrate contour of the crown. 



In the Soricoids (e. g., Proscalops, no. 9) tiie homologies are less clear but the low internal 

 cusp appears to be a pseudoprotocone + protocone. 



as secondary. In Centete.'^ the canines are -sharply differentiated from the 

 incisors, the incisors are small and the skeleton presents many analogies to 

 the flesh-eating Creodonts. The upper molars in Microgale differ from 

 those in Centetcs chiefly in the somewhat better development of the internal 

 basal ridge and in the antero-posterior narrowness of the whole tooth, which 



