208 TEETIAET VEETEBRATA OP THE PATtTM. 



anterior edge of the maxilla. The canine, which was ahout the same size as the 

 incisors, is separated from i. 3 by an interval of ahout -7 cm. ; behind it again there is 

 a diastema of about 2 cm. separating it from a single-rooted tooth, behind which 

 again, and separated from it by a short interval, are four closely crowded alveoli. From 

 the examination of this specimen alone, in which the teeth themselves are w^anting or 

 represented by their roots only, one would come to the conclusion that these four 

 posterior alveoli belonged to the single-rooted ^w. 2, pm. 3, and a double-rooted jim. 4, 

 as they have been marked in the figure ; but Dr. Abel, who has better specimens in which 

 the teeth are preserved, states that in Eotherium the posterior premolars are single- 

 rooted, and that there are in all six premolars, of which the second is lost very early. 

 If this be so, then the alveoli marked pm. 4 in the figure belong to pm. 5 and pn. 6 ; 

 those marked pm. 2 and^?n. 3 to pm. 3 and2???^. 4, while between the pm. 2 and pm. 1 

 of the figure a tooth has been lost and its alveolus disappeared ; it may, however, be 

 remarked that there is only a very short diastema behind pm. 1, while the interval 

 between it and the canine is considerable, so that if a premolar has been lost at all it 

 seems more likely to have been the first of the series. It is possible that the skull 

 here figured may have come from a rather higher horizon than that at which Eotherium 

 proper is found, and that some modification of the teeth in the direction of the later 

 forms may already difi"erentiate it from the animal described by Abel ; possibly it may 

 belong to Abel's new genus Protosiren *, at present undefined. Until that writer's 

 work on these Middle Eocene Sirenians is published, these questions must remain 

 undecided. The molars are three in number ; they are bilophodont teeth, the anterior 

 crest being formed by a large blunt inner cusp and an outer sharper portion composed 

 of two obscurely separated elements. The posterior crest also consists of a blunt 

 inner tubercle and a sharper outer one. From the antero-external side of the antero- 

 internal cusp a ridge runs down to the cingulum, which forms a small shelf-like 

 projection on the anterior face of the tooth : from the postero-external face of the 

 postero-internal cusp a similar ridge runs down to the cingulum of the posterior end 

 of the tooth ; this ridge is best developed in m. 3, where, with the main inner cusp, it 

 gives a V-shaped surface in wear. This type of tooth agrees with the description given 

 by Dr. Abel f of the primitive Sirenian molar, except that the intermediate cusp of the 

 hinder row is very obscurely developed, if at all. 



The dimensions (in centimetres) of this skull are : — 



Extreme length (exaggerated by fractures) 36-5 



Width between outer angles of occipital condyles .... 8*2 



Greatest width of occipital surface 13 



Width oi foramen magnum 4 



Height of occipital surface above foramen mar/num .... 7'2 



* Abel, ojj. cit. p. 146. t Abel, op. cit. pp. 145-46. 



