1882.] 455 [Cope. 



elevated, however, as in that tooth, and thus not so much developed as in 

 Oxymna, Stypolophus, etc. The fourth premolar has a median cutting edge 

 on the short heel. 



Measurements. M. 



Length last four superior molars 022 



" P-m. iii 0065 



" iv 0085 



Width " " 0050 



(anteroposterior 0055 

 transverse 0088 

 oblique external 0072 



_,. ^ -. .. f anteroposterior 0027 



Diameters M. iw ^ „„__ 



\ transverse 0055 



_. ^ • r • -KT T f anteroposterior 007 



Diameters mferior M. I -^ „„_ 



\ transverse 005 



-^. ^ ' c • -KT TT f anteroposterior ' 0055 



Diameters infenor M. II J ^^.o 



I. transverse 003 



Depth of ramus at M. II, (squeezed) 010 



The peculiar characters of the last inferior molar distinguish this species 



from its congeners. The last superior molar is relatively smaller than in 



the D. protenus. In size this species is superior to the I), dawkinsianus, 



and is smaller than the D. leptomylus. It is dedicated to the distinguished 



geologist, Dr. F. V. Hayden. 



New Mexico, D. Baldwin. 



TAXEOPODA. 



CONDTLABTHRA. 



Periptychidae. 



Periptychus rTiaModon Cope. Catathloeus rhabdodon, American Natur- 

 alist, 1881, 829. 



Periptychus earinidens Cope, loc. cit. 1881, p. 337. 



Periptychus ditrigonus Cope, sp. nov. 



This rare species is known from a right mandibular ramus, which ex- 

 hibits part of the symphyseal suture, with the alveoli of the molar teeth, 

 except the first. The only well jireserved crown is that of the second true 

 molar. 



The second true molar presents very peculiar characters, and the man- 

 dibular ramus is shallower and thicker than in the two other species of 

 Periptychus. The former has a wide external cingulum which is 

 not present in the other species, and there are only six cusps 

 instead of seven. These are peculiarly arranged. The anterior three 

 are much as in P. rhabdodon, the anterior being not quite so far in- 

 ternal as the posterior inner, close to it, and as large as the anterior 

 external. The posterior three, are a posterior inner and posterior median 

 as in P. rhabdodon, and a peculiarly placed posterior external. This is not 



