EXTINCT BATRACHIA. 383 



The larger ones where broken at the bases exhibit a moderate puljD cav- 

 ity; the smaller, a large one extending to near the tip. Several, though 

 not all, of the larger teeth display a shallow groove on the external face 

 to near the tip, which is probably owing to pressure and a partial crush- 

 ing. The points of the larger teeth are more abruptly acute, and turned 

 abruptly backwards. A portion of their increased length (.35) is to be 

 attributed to the splitting ofi of the external dentary margin and the 

 exposure of the roots. No alveoli are shown, and the dentition is prob- 

 ably by anchylosis of base. 



A portion of the dentition is well displayed in a specimen (No. 117) 

 which includes the top of the head without muzzle or occiput, with a 

 portion of the side including both mandibular rami. One of these sup- 

 ports twenty-six or seven teeth, which are longest anterior to the middle, 

 and diminish in both directions. A considerable number of maxillary 

 teeth oppose them, while the rather shorter premaxillary teeth are 

 curved towards the slightly posterior end of the dentary bone. All the 

 teeth are uniformly cylindric, except at the extremity, where they are 

 expanded and flattened so as to produce a longitudinal edge, which is 

 carried backwards on a recurvature of the apex. The base is anchylosed 

 equally and without enlargement, and no part of the shaft is striate or 

 grooved. The upper surface of the cranium is narrow, a result not 

 altogether due to pressure, with distinct median suture. The surface, 

 with that of the mandible, is smooth, as in the cranium above described. 

 The mandible exhibits two longitudinal series of foramina. 



It is to be regretted that both the specimens of crania are in such a 

 state as to preclude the proper determination of their elemental seg- 

 ments. 



Length of mandibular dental series, 0.024 m. ; depth of mandible at 

 middle, .005 ; nine teeth in, .005 ; length of longer teeth, .002. 



From the above it appears that the apparent abruptness in change 

 from the longer to the shorter teeth in the skull first described is due to 

 accident. 



Characteristic of the species are the remarkable length and slender- 

 ness of the fan-shaped neural and heemal spines, and the absence of an 

 acute serration on their margins. In this species the spines have a 

 laminiform expansion at the base in their plane. In the Ptynnius pectin- 

 atus, previously described, these spines are not only relatively broader 

 and more fan-shaped, but they are acutely serrate on the margin and 

 constricted at the base. 



An interesting specimen displays the base of tlsye tail, with two inches 



