ORDER IV SAUROPTEEYGIA 171 



Family 1. Ichthyosauridae. 

 J'Fith fhe charaders of the order. Trias to Cretaceous. 



Mixosauras, Baur. Most of the smaller-sized Triassic remains are placed 

 in this genus as distinct from Ichthyosaurus, the teeth being in less uniform 

 series, and the limbs less completely paddle-shaped. The radius and ulna are 

 elongated, and separated by an interstice throughout their length. M. 

 cornalianus, Bassani, the typical species, varies from 0*5 to 1 m. in length, 

 and occurs in the Upper Trias of Besano, Lombardy. 31. ataviis, Quenstedt, 

 is known by fragments from the Muschelkalk of Würtemberg. 



Ichthyosaurus, König (Figs. 262-271). Teeth conical and in uniform series. 

 Kadius and ulna shorter than broad, proximally in contact. Humerus and 

 femur with two concave distal facettes. Total length of largest forms upwards 

 of 10 m. • 



This genus is most abimdant in the Lias, J. communis and I. intermedius being 

 familiär English species. Localities noted for the excellence of their fossil remains are 

 Dorsetshire (Lyme Regis) and Somersetshire in the Lower Lias, and Yorkshire, Cal- 

 vados, Würtemberg (Boll, Holzmaden), and Franconia (Banz, Altdorf) in the Upper 

 Lias ; and the species of the one division are for the most part distinct from those of 

 the other. /. communis, intermedius, latimanus, platyodon, and tenuirostris are 

 especially characteristic of the Lower Lias, and /. acutirostris, ingens, quadricissus, 

 and trigonodon of the upper membe?. Remains of Ichthyosaurus are spai-se in the 

 Middle Jura, but a number of species occur in the Upper Jura of Solenhofen and 

 Kelheim, Bavaria, Northern France, and England. Cretaceous forms are known from 

 England, France, the East Indies, Australia, New Zealand, and Chili. 



Ophthalmosaurus, Seeley. Edentulous or with minute teeth confined to 

 front of the jaw. Humerus and femur with prominent trochanteric ridge 

 and with three concave distal facettes ; all remaining limb bones more or less 

 rounded and separated. Clavicles separated. Upper Jura and Lower Creta- 

 ceous ; England. 



Baptanodon, Marsh (Sauranodon, Marsh non Jourdan). Similar to the 

 preceding, but completely edentulous. Interclavicle not observed ; digit 

 arising from the intermedium consisting of two longitudinal rows of ossicles. 

 Coracoids unite in the median line in large elliptical facettes. Upper Jura ; 

 Wyoming. 



Shastasaurus, Merriam. Includes several large species from the Upper 

 Trias of northern California. Pelvis very robust ; all but first ten ribs single- 

 headed. Cymbospondylus, Leidy, from Middle Trias of Nevada, is imperfectly 

 known. 



Order 4. SAUROPTERYGIA. Owen.i 



■Primitive aquatic reptiles with long neck, lizard-like body, and moderately shorf 

 tail. Cranium small, with parietal foramen and large supratemporal vacuities. 



^ Andrews, ö. W., On Plesiosaurus, Pliosaurus, etc. (Quar. Journ. Geol. Soc. vol. XXXVII. p. 440), 

 1881.— Also ibid. vol. LIII. (1897), p. 177, and vaiious articies in Geol. Mag. [4], vol. II. (1895), p. 241 ; 

 ibid. vol. III. (1896), p. 145 ; Ann. Mag. Nat. Hist. [6], vol. XV. (1895), p. 333 ; ibid. vol. XVI. 

 (1895), p. 429. — Bassani, F., Sui fossili degli schisti bituminosi triassici di Besano (Atti Ist. Veneto 

 Sei.), l8SQ.~Beneden, P. J. van, Deux Plesiosaures du Lias inf^rieure du Luxembourg (Mem. Aead. 

 Roy. Belg. vol. XLIII. p. 1), \8%().—Boulenger, O. A., On a Nothosaurian Reptile referable to 

 Lariosaurus (Trans. Zool. Soc. vol. XIV. p. 1), 1896.— Cope, E. />., On the structure of the skull in 



