30 BULLETIN 34, UNITED STATES NATIONAL MUSEUM 



ceratobyal is eitbei- free at its posterior extremity, as in the Proteida, 

 or in the more typical forms it joius tlie quadrate cartilage by direct 

 articulation or by ligament. 



The byoid apparatus bas a very uniform character in the various 

 families, excepting in tbe OryptobrancbiidiDB, Amphiumidiie, and Coecil- 

 iidae, where it is quite different. In the typical forms it is constructed 

 as follows: lis suspensor is, as usual, the ceratobyal, which is undi- 

 vided. This is connected with a median basal piece, the first basi- 

 branchial, by a segment, generally slender, the hypohyal. Sometimes 

 this piece does not touch the ceratobyal. From tbe posterior lateral 

 border of the basibraucbial there Originates on each side a rod, the first 

 ceratobrancbial, which is continued after a joint, as the first epibran- 

 chial. From a process which originates between the bases of these, on 

 the superior side of the basibraucbial, there originates on each side of 

 its [)osterior extremity another rod, shorter than the first, the second 

 ceratobrancbial. In some genera (ETynobiid*) theie is attached to the 

 distal extrennty of this rod a second one, continuous with it, the second 

 ei)ibranchial. The second basibraucbial is separated from the first, 

 and is situated far posterior to it, not far in advance of the coracoid 

 bones, ft is better ossified than most of the rest of the hyoids, and was 

 called the thyroid bone by Cuvier. That it is the distal extremity of 

 the second basibraucbial is shown by tbe fact that it is continuous with 

 the first by a median rod in the larvne. (Plates 15, 25, 26, 30, 37.) 



The important differences displayed by the different forms of the 

 hyoid in the Urodela may be tabulated as follows. 



I. Median and lateral elements distinct. 



a. Two ceratobrancbial pairs. 



Ceratobyals undivided ; epibrancbials, first and rarely second present. Pseudo- 



sauria Blv. 

 Ceratobyals divided ; epibrancbials, 2, 13, and 4 present. Tremaiodera Duni. 

 aa. One pair of ceratobraucbials. 

 Ceratobyals undivided; epibrancbials, 2, 3, and 4 present. Amj)hiumoidea 

 Cope. 



II. Lateral elements continuous across middle line. 



No median elements J])oda Oppel.* 



The Trematodera, Amphiumoidea, and Apoda contain one family 

 each, viz: the Cryptobranchidne, Amphiumidte, and Ccelciiidte. The 

 value of the differences separating them is diminished by the fact that 

 in the larvse of the Pseudosauria the 1, 2, o, and 4 epibrancbials are 

 present, and the ceratobyal is frequently divided (e. </, Chondrotiis tenehro- 

 sus, Plate 25, fig. 1). 



The subordinate differences presented by the families and genera 

 are indicated under their respective heads. 



The Urodela, excepting the Apoila, have limbs. Tbe toes number 

 from two in both feet to five in the posterior foot, and four in the anterior 

 foot. Eo Urodele agrees with the extinct genus Eryops (Cope), from the 

 *Oppe], IcjLl, not A^jodes of Linuceu.s (in lisbus^; Fseiiduphidla De Bl., 1816, 



