FOSSIL AND liECENT LAGOMORPHA. 471 



specimens of Falceolagus. TIic pattern of less worn teeth, too, is rather different from 

 what occurs in Lejius. In none of the numerous triturating surfaces of Fnlcvolagns- 

 teeth figured do we meet with a transverse fold penetrating so far outward as in the 

 four intermediate teeth of Lcpus, and in the true molars and posterior premolar of 

 Lagomys. This is confirmed by Cope's description : — " The inner side of the four inter- 

 mediate molars is deeply grooved/o;- a short distance " (italics mine; cf. Cope's figures), 

 " which gives a fissure-like notcli on attrition. This disappears after use, as does also a 

 less profound crescentic fossa in the middle of the crown, whose concavity is directed 

 outward " *. 



This statement, in my opinion, does not fully describe the pattern in young specimens, 

 which seems to be very ephemeral in Falcpolagus. In a fragment of the right upper 

 jaw of P. Kaydeni in the Brit. Mus. (5727), of which I give an enlarged figure 

 (PI. 36. fig. 36), the alveolus of the second premolar (p. 2) is sliown, and the three 

 teeth p. 1, m. 1, m. 2 are seen in place. The empty alveolus of the premolar 

 suggests that in its contour this tooth very much approached the corresponding tooth 

 0^ Prolagns oeningensls (PL 36. fig. 21), and to judge from \\hat we find in the following 

 tooth (jj. 1) there is a strong assumption that the pattern of p. 2 of Pcdceolagus also 

 resembled that of Prolagus cen'mgensis. P. 1 of Palceolagus exhibits the internal notch 

 {a) with which we are acquainted in TitoHomys and in the deciduous teeth of Prolagus, 

 Lagomys, and Lepiis, and wliich moreover persists as such ia the premolars of Prolagus, 

 in the second premolar of Lagomys, and in the anterior premolar of Lepiis. In the 

 premolar of Palceolagus we find, on proceeding inward, a crescentic central enamel 

 islet in the centre of the crown, known already from the descriirtions and figures of 

 Leidy and Cope. It is, too, an old acquaintance of ours ; for to all appearance it is the 

 homologue of the large internal enamel-fold {h) of Tltaiiomys, whose fiu'ther history we 

 have followed up in tlie other genera. But this is not all. From the antero-external 

 corner of p. 1 of Pahvolagits starts an enamel-fold in a postero-internal direction, 

 terminating near the outer end of tlie crescentic fold's posterior horn. No mention is 

 made of this outer fold in Leidy's and Cope's descriptions ; it is, however, visible in 

 one p. 2 of Cope's figures (pi. Ixvii. fig. 16 a) ; but I have not seen it delineated for 

 the same tooth together with the crescent fold, as in the figure which I publish. The 

 outer fold just described is undoubtedly tlie homologue of the outer enamel-fold (c) 

 of Titanomys, and I do not doubt that still younger stages of PaUvolagus — which 

 have been figured by Cope, but in an uusatisfectory manner — will show a greater 

 development of both the enamel-folds, and therewith a stronger resemblance to the 

 pattern of the Titanomi/s-teeth and the posterior premolars of Prolagus. 



The true molars of Palceolagvs in the specimen figured exhibit only the crescentic 

 central islet (6) and the internal notch. As stated by Cope in the passage quoted above, 

 and as shown likewise by the illustrations of both the American writers, the internal 

 notch and the crescentic islet are worn away by attrition, without any other change taking 

 place. In this consists the great difference between the American fossil and all the forms 



* Op. cit. p. 876. 



