78 MR. B. LYDEKKER ON A SIRENIAN JAW [Feb. 2, 



unsolved problem of the evolution of the Sirenian order, and that it 

 was accordingly worthy of being brought under the notice of this 

 Society. 



Before proceeding to the description of the specimen a few words 

 are necessary as to the Sirenian remains hitherto recorded from the 

 Venetian Tertiaries. Some years ago the late Baron Zigno' described 

 and figured a certain number of Sirenian remains from the Miocene of 

 Belluno, in the north of Venice, which were referred to four species, 

 under the names of Halitherium bellunense, S. anyustifrons, H. 

 curvidens^ and //. veronense. At a later period these four species 

 were reduced by Professor Lepsius ^, of Darmstadt, to two ; H. 

 bellunense being transferred to Metaxytherium^ while //. angusti- 

 frons and S. curvidens were merged in H. veronense. Since to my 

 mind the distinction between Metaxytheriumsind Halitheriumis not 

 of sufficient importance to be regarded as a jjeneric one, we may, 

 so fiir as this information goes, reckon the Venetian Sirenians as 

 indicating two species of Halitherium, under the names of tl. bellu- 

 nense and H. veronense. 



Vicenza, where the s[)ecimen under consideration was obtained, 

 is situated, I need hardly say, in the south-western half of the 

 Province of Venice, a little north of the parallel connecting Verona 

 and the city of Venice. In spite, however, of its distance from 

 Belluno, it is most probable that the mammaliferous beds of both 

 locahties are of the same horizon ; in which case those of Belluno 

 should be reckoned as Upper Oligocene. 



Of the Sirenians from Venetia the types of Halitherium bellunense 

 and II. veronense exhibit the cheek-teeth in a good state of pre- 

 servation. In the latter species ^ tlie upper j)remoIars are very small 

 teeth, with nearly cylindrical crowns. On the other hand, the upper 

 molars are relatively large teeth, with oblong crowns, carrying two 

 transverse ridges, with fore-and-aft talons. The anterior talon in 

 these teeth is very large and prominent, while the posterior one is 

 considerably smaller. Their first transverse ridge is more nearly 

 continuous than the second. "When somewhat worn, as is the case 

 with those of the type specimen, these transverse ridges show nearly 

 straight bands of deritine, and not the distinct trefoils observable in 

 the molars of Halithei-iitm schinzi from the Oligocene of Hessen- 

 Darmstadt. A distinct tubercle occurs in the inner half of the 

 median transveise valley of these teeth. In Baron Zigno's figures 

 there is no indication of what I shall allude to as a masked sele- 

 nodont structure in these molars. 



Coming now to the consideration of the specimen forming the 

 subject of this communication, of which a representation of the teeth 

 is given herewith (see fig. 1, p. 79), it may be observed, in the first 

 place, that it is a fragment of the left maxilla of a very young mamninl 

 of comparatively large size. It shows part of the j)alatal surface, the 



' Mem. E. 1st. Veneto, vol. xviii. pp. 438-449, pis. xiv.-xviii. (1S75) ; see 

 also Zifino, op. cit. vol. xxi. pp. 291-298, jil. iv. (1880). 



■■^ Abliandl. inittolrheiii. geol. Vereiiis, vol. i. ])p. 1-179, jjls. i.-x. (1881-82) ; 

 see also Capellini, Mem. R. Accad. 1st. Bologna, ser. 4, vol. vii, pp. 39-53 (1886). 



^ Ziguo, oj}. cit. vol. xviii. pi. xviii. 



