MORPHOLOGICAL REVISION 87 



quadrate is short and thins out rapidly upwards, being closely united with the 

 squamosal. Its condyle is set at an angle of 45 with the axis of the skull, and 

 consists of one flat and one convex surface; continuous but forming a deep angle 

 together. Exterior to the exoccipital, and interno-inferior to the intercalare, is a 

 small distinct element, apparently in the position of an opisthotic or external occipital. 



"The excavation for the auditory apparatus appears to be in the exoccipital. 

 It is almost entirely filled by what I suppose to be a large stapes. This bone is in 

 shape like a compressed flask, with the head directed inwards and forwards, and 

 its inferior edge produced into a prominent keel, which is produced into a point 

 below, and free from the neck of the flask. The head is truncate and is separated 

 from the internal cranial wall by a narrow interspace. Its external extremity is 

 not absolutely perfect in the specimen, but does not appear to have extended in 

 an ossified condition beyond the exoccipital bone. In a specimen of Empedias 

 molaris* there is a meatus auditorius, in which the stapes was not found on cleaning 

 out. This element is coosified with the surrounding bones laterally and posteriorly. 

 Consequently when broken open, the vestibule is represented by two deep grooves, 

 directed inwards and anteriorly." 



In 1892 Cope (35) says: 



"Chilonyx agrees with the Stegocephalia and with other Diadectidce in posses- 

 sing a distinct intercalare {tabulare). The component elements of the cranial roof 

 are equal in number and similar in position to those of the Stegocephalian skull, 

 except that the supramastoid (squamosal) extends between the parietal and inter- 

 calare {tabulare) to the posterior border of the cranial table; and the supraoccipital 

 does not extend onto the superior face of the skull, except as a narrow border. 

 The quadrate bone is directed forwards instead of posteriorly, which causes an 

 anteroposterior abbreviation of the supratemporal and squamosal elements. The 

 elements of the temporal roof are not exclusively tegumentary, but are identical 

 in character with the bones of the brain case, and the sutures are visible on the under 

 as well as the upper side." 



In this paper he gave figures of the skull of Chilonyx. These figures were 

 republished several times (36, 42, 44). 



A comparison of Cope's figure with that worked out by the author, in collabora- 

 tion with Dr. Broom, shows that the two interpretations do not agree. There are 

 but two bones over the temporal region, not three; the condition is the same as in 

 Diadectes, and Chilonyx can only be considered a very specialized genus of the 

 same family. Cope's description of the posterior surface of the skull is erroneous, 

 as is his figure of the quadrate region (plate vm, fig. 6, Proc. Am. Phil. Soc, vol. 

 xxxiv). It resembles in all respects the same region in Diadectes. 



A single successional tooth just coming into place shows a single terminal cusp. 



Bolbodon tenuitectus Cope. (Plate 10, fig. t ; text fig. 35, A.) 



Characteristic specimen: The type, No. 4375 Am. Mus. Nat. Hist. Cope Coll. 

 The sculpture of the skull is very much less rugose than that of Diadectes phaseohnus. 

 The portion of the quadrate region preserved indicates that the tabulare is united 

 with the squamosal, but as the sutures can not be made out this point is uncertain. 

 The bone described by Cope as a turbinal is the same in position and relations as 

 that described by Swinnerton and Howes in Sphenodon and by the author in Dime- 

 trodon as a septo-maxillary. The bones described by Cope as palatines are the 

 anterior ends of the prevomers. The molar teeth were apparently without cusps, 



* Figured in Proc. Amer. Philos. Soc. vol. xix, p. 56. 



