ORDER II 



SQUAMATA 



153 



foramen present ; premaxillae and nasals fused into a simple rostrum; quadrate 

 large, perforate, and movably attached to squamosal and prosquamosal ; parietal un- 

 paired and joined to the supraoccipitals and probtics by decurved lateral processes. 

 Mandibular rami united at the symphysis by ligament, and with a movable articulation 

 behind the middle of each ramus. Teeth large and conical, fixed by tumid bases in 

 shallow alveoli of the jaw-bones and pterygoids. Sclerotic ring present. Vertebrae 

 procoelous, cervicals tvith hypapophyses. Sacrum wanting; sternum probably never 

 ossified ; interclavicle (episternum) sometimes present, but no clavicular arch. Limb- 

 bones short, but the digits are lengthened by an increased number of phalanges, the 

 ungual ones clawless. 



The vertebral column comprises 115-130 or perhaps more procoelous 

 vertebrae, and is sometimes divisible into cervical, dorsal, lumbar, and caudal 

 regions. The distinction between dorsal and lumbar series is not very decided, 

 however, except that the latter bear shorter ribs. The transverse processes 

 are short and thick in the precaudal vertebrae for the attachment of single- 

 headed ribs; in the caudals they are flattened and elongated but not costiferous, 

 and become obsolete at about the middle of the tail. The neural arches are 

 always, even in young individuals, thoroughly coossified with their centra; the 

 neural spines are of moderate length, but sometimes notably elongated in the 

 posterior region of the tail. The zygapophyses are strong in the cervical and 

 anterior thoracic region, but become weaker and finally disappear in the tail. 

 Y-shaped haemapophyses or chevron bones are present in all the caudals with 

 the exception of the first five or more, to which the name " pygals " has been 

 given ; each chevron articulates 

 vith its own centrum. The 



only with its own centrum. The 

 atlas is composed of a wedge- 

 shaped intercentrum below, and 

 two lateral pieces or neuropo- 

 physes, as in lizards, its centrum 

 being represented by the odontoid 

 process of the axis. A wedge- 

 shaped intercentrum occurs be- 

 tween the atlantal intercentrum 

 and the axis. The axis and five 

 following cervicals bear each a 

 more or less stout exogenous 

 hypapophysial process, to the ex- 

 tremity of which is attached a 

 small, free epiphysis, correspond- 

 ing morphologically to an inter- 

 centrum (Fig. 242). This is 

 wanting in the last cervical, and 

 the process itself is rudimentary. 



The skull (Figs. 243, 244) 

 resembles that of Varanus more 



F 



z- 



FlG. 242. 



Clidastes stenops, Cope. Upper Cretaceous ; Kansas. An- 

 terior cervical vertebrae .-I, From the side. /;, From in 

 front, !/ 2 . (c, Centrum ; d. Transverse process; h, Hypapo- 

 physial epiphysis or intercentrum; hy, Hypapophysis ; jn:. 

 Prezygapophysis ; sp, Neural spine), (after Cope). 



nearly than that of other living reptiles. The parietals, frontals, and pre- 



rank and affinities of the Mosasauridae (Quar. Journ. Geol. Soc. vol. XXXIII. p. 682), 1877.— Ibid 

 vol. XXXIV. (1878), p. n8.— Williston, S. W., On Mosasaurs, etc. (Kansas Univ. Quar. vol. ii. p. 

 83), 1893. — Ibid. vol. III. (1895), p. 165.— University Geol. Surv. Kansas, vol. IV. Topeka, 1898. 

 — Williston, S. W., and Case, E. <'.. Kansas Mosasaurs (Kansas Univ. Quar. vol. I. p. 1), 1892. 



