1891.] HELODERMA HORRIDUM AND H. SUSPECTUM. 117 



Although fully admitting the name Pythonomorpha ^ to have been 

 ill chosen, I cannot but agree with Prof. Cope in maintaining the 

 Mosasaurs as a suborder, if only for the hyperphalangy of their 

 limbs ^ and the type of their dentition, the large osseous bases which 

 bear the teeth being inserted in a groove of the jaws, a feature 

 which may be regarded as midway between the thecodont and acro- 

 dont types; whereas the Monitors and Heloderms belong to the 

 pleurodont type. The HelodermatidcB on the other hand are true 

 Lacertilia, more closely related, in my opinion, to the Angiiidce than 

 to the Varanida. And although there are undoubtedly many points 

 common to the Monitors and the Mosasaurs, I hold that Dr. Baur 

 is mistaken in proposing to revert to the Cuvierian views o the 

 affinities of the large extinct marine Reptiles. Dr. Baur says : " It 

 is evident that the Mosasauridce are very closely related to the 

 Varanidis. They simply represent highly specialized aquatic forms." 

 Does this mean that limbs so strongly specialized as those of the 

 Monitors can have been modified into the paddles of the Mosasaurs ? 

 A glance at the figures (see fig. 6, p. 118) suffices to refute such a 

 theory. But we can perfectly well conceive the hind limb of a Doli- 

 chosaurian becoming modified into the said paddle ; and I can see 

 no reason for not regarding these Cretaceous Lizards as the pro- 

 genitors of the Mosasaurs, and at the same time of the true Lacer- 

 tilia of which the Pleistocene and recent Varanidce are a family. 

 This view is besides in accordance with the suggestion made by 

 Dollo^, that the progenitors of the Mosasaurs must have possessed 

 the zygosphenal articulation. 



The Order Squamata may very well be divided into the following 

 five Suborders, merely with regard to the structure of the limbs and 

 vertebral column : — 



A. Pectoral arch or its rudiments present. Caudal hypapophyses 



forming chevrons. 

 L Dolichosauria. 15-1/ cervical vertebrae. Extremities 



(Fig. 6 A, p. 118) archaic, i. e., approaching the Batrachian 



type. 

 n. Pythonomorpha. 9 or 10 cervical vertebrae. Extremities 



(Fig. 6 B, p. 118) paddle-shaped, with hyperphalangy. 

 IIL Lacertilia. 8 or 9 cervical vertebrse. Fibula reduced 



proximally ; fifth metatarsal reduced in length and strongly 



modified (Fig. 6 C, p. 118). 



IV. Rhiptoglossa. 5 cervical vertebrae. Extremities pincer- 

 shaped ; all the metatarsals reduced in length and strongly 

 modified (Fig. 6 D, p. 118). 



B. No trace of pectoral arch. Caudal hypapophyses disconnected 



distally. 



V. Ophidia. 



^ Pythonomorijha, Cope, \?>Q'd,=Mosasaur%a, Marsh, 1880. 

 ^ At least three phalanges in digit I. 

 ^ Bull. Soe. Beige Geol. iv. 189U, p. 167. 



