EXTINCT BATRACHIA. 365 



the smallest, and originate immediately in front of the occipital con- 

 dyles and diverge outwards and backwards. They are little curved, sub- 

 cylindric, and slightly expanded at the extremities. , 



Of the pleural elements the first and second are little curved, and the 

 first is marked by a pit or foramen on the under side near the distal end, 

 which is clearly visible on both sides of the specimen. The third and 

 fourth pleurals are more curved, and the outer ends slightly expanded 

 and directed backwards. 



The obverse of the specimen shows that the anterior axialhyal is 

 wedge-shaped. The lateral basihyals are massive. The second haemal 

 branchihyal is dilated, fan-shaped distally, and supports two pleural 

 elements. The muzzle projects over the lower jaw, and was rather 

 broadly truncate. The premaxillary teeth are cylindric and six in 

 number on each side. The maxillary bone is represented by a lamina 

 at each lateral extremity of the premaxillary. The mandibular rami 

 are very stout, as are also the ceratohyals. The vertebrae have possessed 

 some apophyses, apparently keel-like diapophyses. The ribs are slightly 

 curved. 



Length of head and eight vertebrae, .0335 m. ; of head, .0152; expanse 

 of mandibular rami, .013; length of left ceratohyal, .0086 



Thyesidium, Cope. 



Established on a species which presents its principal peculiarities in 

 the structures of the vertebrae. Two specimens present inferior views of 

 the spinal column, showing that the genus possesses, like Siren, enlarged 

 diapophyses, but that they are peculiar in their fan-like form. They re- 

 semble slightly the caudals of Ptyonius, but are present on the dorsal 

 vertebrae. Whether the latter possess ornamented neural spines the 

 specimens do not indicate. The abdomen is protected by the usual hair- 

 like rods arranged en chevron, the angle directed forwards. No indica- 

 tions of limbs can be discovered on the blocks. 



Without the cranial bones the afiinities of this genus can not be deter- 

 mined ; while it may be allied to Cocytinus, the vertebrae of that form 

 are without the peculiar diapophyses. 



Thyrsidium fasciculare, Cope. 



The best preserved example of this salamander includes nine verte- 

 brae and the corresponding ventral armature. The centra, seen from 

 below, are much contracted in their form, presenting an obtuse median 



