152 REPTILIA class in 



Order 2. SQUAMATA. (Lepidosauria, Streptostylica.) ^ 



Body elongate, covered loitli corneous, or more rarely -with dermal sccdes or scutes. 

 Quadrate movably attached to the skull ; the lower ter)iporal arcade always, and upper 

 temporcd arcade frequently wanting. Palatal vacuities large, pterygoids not in contact 

 with vomer ; external nares separated ; teeth acrodont or pleurodont. Vertebrae well 

 ossified, usually procoeloiis, rarely amphicoelous ; sacral vertebrae not more than two in 

 number. Post-cervical intercentra and abdominal ribs wanting ; dorsal ribs single- 

 headed. Limbs adapted for ambulation or natation, absent only among Ophidia and 

 a few Lacertilia. 



This order comprises Lizards, Snakes, and two extinct groups of aquatic 

 reptiles, — Dolichosauria and Pythonomorpha, — the earliest clearly recognised 

 members of which occur in the Cretaceous. The Sguamata are evidently very 

 closely allied to Rhynchocephalians, and in all probability their origin is to be 

 traced to that group. 



Sub-Order 1. DOLICHOSAURIA. 



Small, aquatic, serpentiform reptiles, with toell-developed lizard-like limbs and limb- 

 girdles. Vertebrae procoelous, and articulated both by zygapophyses and zygosphene- 

 zygantrum arrangement. Sacral vertebrae not anchylosed. Mandibles with sutural 

 symphysis. Teeth pleurodont. 



The family Dolichosauridae comprises a few genera from the English Chalk 

 and the Upper Cretaceous of Istria and Dalmatia, the largest of which attain 

 a length of between two and three metres. JDolichosaurus, Owen, has no less 

 than seventeen cervical vertebrae and large hollow ribs. Acteosaurus, Adrio- 

 saurus, Aigialosaurus, Carsosaurus, Pontosaurus, and Mesoleptos are allied Istrian 

 genera. Most of the detached vertebrae of Cretaceous age, commonly classed 

 as Ophidian, are doubtless Dolichosaurian. Like the Pythonomorphs, these 

 forms probably passed away without leaving any post-Cretaceous descendants. 



Sub-Order 2. PYTHONOMORPHA. Cope. 2 



Large marine reptiles ^vith elongate body and two pairs of pxcddle- shaped appen- 

 dages. Skull lizard-like, elongate, depressed; superior temporal arcade and pinecd 



^ Co2)e, E. D.. Crocodiles, Lizai-ds, aud Snakes of North America (Ami. Ke^jt. Smithsonian Inst., 

 1898), 1900. 



^ Literature : 



Baur, G., Morphology of the skull of the Mosasauridae (Journ. Morphol. vol. XII., No. 1), 1892. 

 — Cojje, E. D., The Reptilian orders of Pythonomorpha and Streptosauria (Proc. Boston Soc. Nat. 

 Hist. vol. XII. p. 250), 1869. — The Vertebrata of the Cretaceous Formations of the West (Kept. 

 U.S. Geol. Surv. Territ. vol. II.), 1875. — Professor Owen on Pj'thonomorpha (Bull. U.S. Geol. Surv. 

 Territ. vol. IV. ]i. 299), 1878. — Ouvier, G., Sur le grand animal fossil de la craie de Maestricht 

 (Ann. Mus. d'Hist. Nat. vol. XII.), 1808. — DoUo, L., Note sur I'osteologie des Mosasauridae (Bull. 

 Mus. Ptoy. d'Hist. Nat. Belg. vol. I.), 1882.— Ibid. vol. IV., 1885.— Nouvelle Note, etc. (Bull. Soc. 

 Belg. de Geol. Pal. et Hydro!, vols. III.-VII.), 1889-94. — Gibbes, R. W., A Memoir on Mosasaurus, 

 etc."(Smithson. Contr. Knowl. vol. II.), 1864.- — Goldfuss, A., Der Schadelbau des Mosasaurus (Nova 

 Acta Acad. Caes. Leop. Car. nat. cur. vol. XXI.), 184-3. — Leidy, J., Cretaceous Reptiles of the 

 United States (Smithson. Coutrib. Knowl.), 1864. — Extinct Vertebrate Fauna of the Western Terri- 

 tories (Rept. U.S. Geol. Surv. Territ. vol. I.), 1873. — Marsh, 0. C, Characters of Mosasauroid 

 Reptiles (Amer. Journ. Sci. [3], vol. I.), 1871.— Ibid. vol. III. (1872) ; and XIX. {1880).—Merriam, 

 J. C, Die Pythonomorpha der Kansas Kreide (Palaeontogi". vol. XLI.), 1894. — Osbo-rn, H. F., A 

 complete Mosasaur Skeleton (Mem. Amer. Mus. Nat. Hist. vol. I. pt. 4), 1899. — Owen, R., On the 



