PAL^EOMASTODON PARVUS. 
163 
of a larger outer and a smaller inner tubercle ; there is a small intermediate tubercle 
in the anterior valley, but otherwise accessory tirbercles are wanting ; the enamel is 
very smooth and the cingulum practically absent. M. 2 is trilophodont, but the last 
ridge is much smaller than the others ; it consists of an outer larger and a smaller 
inner cusp. So far as their molar pattern is concerned, both this species and P. headnelli 
seem to be more primitive than P. ivintoni ; but, on the other hand, P. headnelli by its 
larger size, and both it and the present species in the elongation of the mandibular 
rami, seem to be somewhat more specialized. This intermingling of primitive and 
more specialized characters is to be expected in a group represented by several 
Text-fig. 55. 
Right ramus of maudible of Palceomastodon parvus. Type specimen. About 1 nat. size. 
contemporary species and undergoing rapid change in a given direction, the final 
product, in this instance Tetrahelodon or some closely similar form, being the resultant 
of the various modifications, and in this case combining increased length of the 
mandible with more complicated molar structure. 
Form. & Loc. — Fluvio-marine beds (Upper Eocene) : north of Birket-el-Qurun. 
M. 8479 a. Right mandibular ramus, imperfect at both ends: pm. 3 & 4 are greatly crushed and 
TO. 1-3 much worn. Type specimen figured (text- figs. 50 C, 55) . The mental foramen is 
beneath the anterior end ofpm. 3, and the posterior end of the symphysis is about 5' 5 cm. 
in front of that point. The dimensions of the teeth are given in the table on page 169. 
The depth of the mandibular ramus beneath to. 2 is 7‘2 cm., in front oi' pm. 3 6’6 cm. 
Presented hy Tl'. E. de Winton, Esq., 1903. 
M. 8847. Almost unworn third lower molar. Presented hy the Egyptian Government, 1904. 
M. 8846. Right upper molar (? second) almost certainly belonging to this species. 
Presented hy the Egyptian Government, 1904. 
Probably several of the smaller teeth and jaws in Cairo may belong to this species, but further 
examination of the material there would be necessary to determine this. 
Y 2 
