Figs. 7-8. — Periptychus coarctatuB, last two premolars and first tnip molar of the inferior series, external 

 side; a, inttTiial side; b, superior view. 



The al)ovc spocimens were received too late for description in the body of this volume. Hence 

 I append the following from the proceedings of the Philadelphia Academy of July, 1883 : The 

 characters of the species are well marked in the premolar and molar teeth. The former lack the 

 anterior and internal ledges of the P. carinidens and P. rhahdodon, having only a prominent ledge- 

 shaped heel, besides the principal conical cusp. The true molars lack the small tubercle which is 

 between the pair of threes which compose the crown. The adjacent cusps of the threes are con- 

 nected by low longitudiual ridges instead of oblique ones. The cusps themselves are closer together 

 than in the other species, especially those of the anterior three, which are closely approximated. 

 The anterior one is small and low. The enamel is grooved as in the other species. 



Diameters of crown of fourth premolar: anteroposterior, .0115; transverse, .0115; elevation 

 (worn), .010. Diameters of crown of second true molar: anteroposterior, .011; transverse, .009. 

 From the Lower Puerco beds. D. Baldwin. 

 Fig. 9. — Zetodon gracilis, two fragments of the mandibular ramus, external view, natural size ; a, the 

 same, twice natural size, from above. 



I append the following description of this specimen, as it is not contained in the preceding pages : 



This genus and species are founded on a broken lower jaw which contains the second and part of 

 the lirst true molars, and the fourth premolar. The teeth are of very peculiar character. True molars 

 consisting of narrow crescents in two pairs, which are both concave towards each other, embracing 

 a fossa. The posterior crescents soon unite on attrition, closing the fossa, while the anterior are 

 well separated, and only unite by their anterior apices. Each molar has a small columnar heel. 

 Fourth premolar with the posterior pair of crescents only, which soon unite. The anterior pair is 

 represented by a part of the external one, which forms a narrow lobe. The heel is larger than in 

 the true molar. 



The position of this genus it is impossible to determine from the specimens in my possession. It 

 may be Marsupial or Condylarthrous, and if the latter, one of the Periptychida ; but if not of these 

 groups, its position is not likely to be in any known order of the tertiary periods. 



Char. Specif. — Crowns compressed, deeply grooved at the points of junction of the crescents. This 

 is effected by a narrow lamina from the anterior inner to the posterior outer; the anterior outer 

 bein" free posteriorly, excepting after considerable wear. A groove on the external side of the 

 crown distinguishes the heel, which sinks into the crown below. It is larger on the first than on 

 the second molar. The heel of the fourth premolar is elevated on its posterior edge. No cingula 

 except a weak one at the exterior base of the posterior lobe of the true molars, and at the anterior 

 base of the anterior lobe of the fourth premolar. Ramus compressed ; but little of it preserved. 

 Diameters of p. m. iv. : anteroposterior, .0055; transverse, .0020; of second true molar: anteropos- 

 terior, .0045; transverse, .002. From the lower red bed of the Upper Puerco epoch. D. Baldwin, 

 discoverer. 



