IQO S. W. WILLISTON. 



ation of a compound arch. One thing seems very probable, if 

 this bone is the prosquamosal, then the Squamata have nothing 

 to do with the rhynchocephaloids, but represent a separate and 

 distinct phylum of their own. I prefer to call the bone articu- 

 lating with the postorbital the squamosal, the bone which in all 

 other reptiles articulates with the postorbital behind. 



Of course, if this is the real squamosal, the posterior element 

 cannot be a squamosal, though Koken J thought to solve the diffi- 

 culty by calling the two bones squamosal I. and squamosal II. 

 The history of the contention between Cope and Baur 2 as to the 

 identity of this bone is too fresh in the minds of anatomists to 

 need repeating here. Baur vigorously urged that the bone at 

 the end of the suspensorium is the squamosal, but Baur never 

 fully understood the relations of this bone in the mosasaurs, as is 

 evidenced by his faulty description of it. 3 As Cope has repeat- 

 edly affirmed, 4 and as I have confirmed, 5 the so-called squamosal 

 of the mosasaurs is intercalated between the exoccipital and 

 petrosal, extending far inward nearly to the surface of the brain- 

 case. It needs but a moment's consideration by any one familiar 

 with the relations of the bone in these animals and in the mam 

 mals to be convinced that such remarkably different conditions 

 cannot be those of the same bone. The inner part of the 

 "squamosal" corresponds quite well with the outer part of the 

 paroccipital, or opisthotic element, which was not found in the 

 lizard embryo by Parker. Referring now to the figures of Pro- 

 coloplwn and Pareiasaiinis, it will be seen that the outer part 

 will correspond fairly well with the one called the epiotic. " In 

 some of the genera of Stegocephalia the paroccipital is free from 

 the exoccipital ; in others (Mastodonsaurus} it is coossified with 

 the exoccipital. The paroccipital is in relation to a dermal plate 

 which is very improperly called the epiotic. I propose the name 

 ' paroccipital plate' for it." 6 It may be objected that the pres- 

 ence of an epiotic bone in the lizards is a far too primitive char- 



1 Zeitsch. Deutsch. Geol. Gesellsch., XLV., p. 363, 1893. 



2 Amer. Nat., 1895, 1896. 



3 Jour. Morphology, VII., p. 14, 1892. 

 * Trans. Amer. Phil. Sor., XVII. , p. 19, 1892. 

 s Univ. Geol. Sitrv. A'ans., IV., p. 121, 1898. 

 6 Baur, Journ. Morph., III., p. 469, 1889. 



