MASTODON TEETH FROM PERIM ISLAND. 
5—153 
Relationship of M. perimensis and M. pandionis to one another and to 
OTHER SPECIES. 
It has been shown in the first volume of the present work that M. 'perimensis is a 
species provided with a comparatively short mandibular symphysis with small tusks 
(pi. XLIII.), while that of M. pandionis (pi. XXXVI.) is unusually elongated and 
often furnished with large tusks ; and as it is known that all the early mastodons 
like M. angustidcns and M. longirostris had long tusked mandibular symphyses, while 
the stegodont and more specialized elephants all have extremely short and tuskless 
ones, it is quite evident that evolution has tended to the shortening of the mandibular 
symphysis and the suppression of the mandibular tusks ; and it is therefore also 
pretty evident that the tetralophodont M. perimensis is a more specialized form than 
the trilophodont M. pandionis^ which is considered to be an offshoot from the stock of 
M. angustidens} The circumstance that M. pandionis occurs in the lower Siwaliks 
where M. perimensis is not found is another circumstance pointing to the conclusion. 
If now the tooth of M. perimensis rej^resented in plate XVI., fig. 2, be compared 
with that of M. pandionis represented in figure 1 of the same plate, it will be seen 
that it merely requires the anterior accessory columns (a, a) of the latter to be some- 
what less developed, which would render the valleys more open, and a fourth ridge 
to be developed in the ‘ intermediate’ molars (vol. I., pi. XXXVa.), and a fifth ridge 
and double talon in the last molar {ibid') to transform the trilophodont molars of M. 
pandionis into teeth very like the tetralophodont ones of M. perimensis. Both species 
agree in the presence of cement in the valleys, and it is probable that both were 
furnished with premolars. Taking all these circumstances together, it is by no 
means improbable that M. perimensis may be a specialized descendant from the stock 
of M. pandionis. 
It has also been shown in the first volume (pages 226-7) that the last lower 
molars of the ujiper Siwalik M. sivalensis present a remarkable resemblance to those 
of M. pandionis ; and as the former is evidently a more specialized form — having a 
short mandibular symphysis and no lower tusks, with a tetro-pentalophodont ridge 
formula — it is quite possible that this species may likewise be a descendant from the 
M. pandionis stock ; the development in this instance having tended to an increase in 
the alternate arrangement of the columns, and to the still more complete blocking of 
the transverse valleys ; while the premolars and cement in the molars have dis- 
appeared. This line of development is entirely away from the direction of the 
stegodont elephants. 
Mastodon pandionis also presents a strong resemblance to the Pikermi M. pentelici? 
Thus both species are trilophodont forms, having a long and tusked mandibular 
symphysis, and teeth of the same general plan of structure, with a rugose enamel, 
and some cement in the valleys. The earlier upper teeth of M. pentelici appear. 
1 Supra, page 31. 
2 Gaudry, “ Animaux Fossiles et Geologie de I’Attique,” pis. XXII. -III. 
