THE BATRACHIA OF NORTH AMERICA. 223 



inactive life consequent on parasitic habits. The same result has be- 

 Jalien the Lacertilian family Amphisbaiuidoe and the Ophidian famil}^ 

 of Typhlopida). Both of these are, like the Cseciliidce, parasitic in ants' 

 nests, and both have become nearly blind and have lost their organs of 

 progression, whether limbs or abdominal scales. To aid them in their 

 dark habitat a peculiar tentacle has been developed in this family, 

 which issues from a canal of the maxillary bone. This canal passes 

 irom the orbit, and the tentacle which occupies it is furnished with a 

 muscle and nerve (Weidersheim). It is probably homologous with the 

 '■'■ balancer" of the urodelous larva, which sometimes persists as a non- 

 retractile tentacle in several of the species of the salamaudrine genus 

 Spelerpes. 



The Cisciliidte have been divided into a number of genera by Peters. 

 The presence or absence of minute scales defines some of these, and 

 tlie form and position of the tentacular opening others. Some of the 

 latter do not appear to the writer to be well founded. 



iSTo species of the Cajciliidee enters the geographical boundaries of the 

 nearctic realm. 



Plate 11 represents the skull and some vertebrae of the Clithonerjjeton 

 indistmctum, R. & L., a representative of the family from Brazil. 



TRACHYSTOMATA. 



Yomeropalatiue bones wanting. Supraoccipitals, intercalaria, and 

 basioccipitals wanting. Maxillary bones wanting. Propodial bones not 

 coossified; caudal vertebrai distinct. 



This order, which was proposed by Miiller, has but few living repre- 

 sentatives, nor has paleontology disclosed with certainty any extinct 

 ones. The range of its variation being thus unknown, I confine my- 

 self chiefly to a discussion of the characters of the only family which 

 it contains, the Sirenidtie. The order is distinguished, as above indi- 

 cated, by the absence of many bones of the skull usual in vertebrata 

 and Batrachia — a result which is apparently due to a long process of 

 degeneracy. 



SlEENIDJi:. 



Vertebroeamphicoelous; pterygoidea wanting; premaxillary andden- 

 tary bones toothless: patches on the parasphenoid : two pairs of cera- 

 tobranchials ; a second basibranchial continuous with the first ; several 

 epibranchials; no otoglossal ; the stapes not directly connected with 

 the quadrate; mandibular articulation by a ball-and-socket joint, the 

 ball on the mandible, the cotylus in the quadrate. 



In the known genera of the family the nasal bones are embraced by 

 the spines of the premaxillary bone ; the vomeropalato-pterygoid arch 



