VERTEBRATE REMAINS, PORT KENNEDY BONE DEPOSIT. 203 



would be If; not one of them, however, is isolated, the dentine being continuous 

 round the entering angles of enamel. The failure of these angles to reach the 

 enamel margin of the side toward which they are directed, and an approach to 

 parallelism of the entering and projecting enamel plates produce a triturating sur- 

 face, having the form of a succession of Ws. This is the reverse of what occurs in 

 Anaptogonia rutila according to Prof. Baird, where the triangles become confluent 

 at their bases, thus extending all across the crown ; the same thing is seen in the 

 posterior inferior molar in all the species. There is no trace of roots to these teeth 

 or that previously described. Length of crown of second molar, m. .0056. 



A third specimen is represented by the molars of both maxillary bones, much 

 broken, the posterior of one of the series only being entire. This tooth is slightly 

 curved, and exhibits three ridges on one side, and four on the other ; triangles 1^ 

 and a short loop with two basal angles, the inner more prominent than the other. 

 None of these triangles are isolated, but are rather angular expansions of the con- 

 tinuous dentine. The two inner angles are much more prominent than the outer, 

 but in old age they would probably be equal, judging from their appearance at the 

 base of the tooth ; viewed from below, they appear to be closed ; showing that the 

 character of the group Anaptogonia in this respect is derived from a " retardation " 

 of growth in a point which is early attained in true Arvicola. 



Measurements. 



mm. 

 Length of tooth ; 5 



Length of crown ; 3 



Width of palate ; 4 



SYCIUM Cope. 



Crowns prismatic, the common pulp cavity with lateral bony walls which close 

 the lateral grooves, but do not close the pulp cavity below ; no roots. 



The position of this genus is exactly between Anaptogonia and Microtus, and 

 represents the steps by which the latter was developed from the former. One spe- 

 cies is known to me, which does not differ much in size from the Anaptogonia 

 hiatidens. 



Length of crowns of inferior molars, 9.4 mm. ; S. cloacinum. 



Svcium cloacinum Cope. [Type No. 147, Mus. Acad. Nat. Sci.] 



Two individuals of this species are indicated by the specimens preserved by 

 Mr. Mercer. These include, the first, the m^ and m^ ; the second the mJ- and m^. 

 As usual in this group the molars diminish in size posteriorly. The triangle 

 formulas are: m- 1 -, If; m-^, If; m^, If + 3 lobes. 



In the m 1 the triangles of one side are acute-angled ; and of the other, obtuse- 

 angled. The posterior triangle presents an angle posteriorly as well as laterally. 

 In the m^- the same characteristics exist, with the addition that the anterior 

 (terminal) triangle has its acute column pinched together, but not so as to exclude 

 the dentine. In the m^ the entering angle (groove) of one side enters the triangle 

 of the other side opposite to it, so as to destroy its triangular character. The 



