Cope.] °^ "April .5, 



yond the fourth. The extremities of the crests extend obliquely to their 

 bases, and support four or five dentiform processes. The dense shining layer 

 extends inwards as far as the bases of the serrate portions. The inner 

 face of the anterior crest is oblique, and the posterior inner border curves 

 outwards to behind the first crest, leaving a shelf-like continuation of the 

 palatal surface of the tooth. 



Measurements. M. 



Length of tooth 038 



Width at third crest 015 



Depth opposite third crest 004 



This species must be compared with G. fossatus Cope, and C. serratus 

 Newb. The latter is a wide tooth with less oblique, and fully serrate 

 crests. The former is a narrow species, but the anterior crests are not 

 nearly so extended ; it is deeper, and the inner side is vertical, and with- 

 out the posterior palatal lamina seen in the two species named. 

 Ctenodus etalophus. Sp. nov. 

 Represented by a single left tooth in excellent preservation. Its charac- 

 ters are very marked. It is of narrow form, and has more numerous crests 

 than any other known American species. They number ten, and there are 

 two or three other ruclimental ones at the posterior extremity. They are all 

 more transverse than usual, five being directed forwards, and five slightly 

 backwards. The crests are acute, but the grooves and emarginations are 

 not very deep. The crests are entire, except at the obliquely truncate dis- 

 tal extremities, where there are from two to four dentations. The shining 

 layer does not extend within these. The inner border of the tooth is ver- 

 tical, excepting posteriorly, where the inner border of the crest-bearing 

 portion turns outwards, leaving a narrow ledge of the palatal face. The 

 latter is concave in cross section. 



Measurements. . M. 



Length (.004 at one end inferential) 033 



Width at fifth crest 010 



Depth opposite fifth crest. 004 



It is not necessary to compare this species with any other. 

 Observations on the Pelycosaurja. 



In addition to the type of humerus described under the head of the genus 

 Clepsy drops, several other remarkable forms occur in the collection, which 

 are probably referrable to the various genera of Pelycosauria. I give 

 the following tabular analysis of them : 



A. No condyle ; a supracondylar foramen. No special proximal articu- 

 lar surfaces. 

 No. 1. {Clepsy drops) Specimens ,5 . 



A A. Condyles and supracondylar foramen. 

 a. The shaft uninterrupted. 



No. 2. Condyles longer ; smaller Sp. 6. 



No. 3. Condyles wider ; larger Sp . 4. 



