SAUROPTERYGIA. 167 



FIG. 106. 



DIAGRAM ILLUSTRATING THE PRINCIPAL CHARACTERS OF THE PLESIOSACBIAN 



REPTILES. 



A, B, C. Plesiosaurus macrocephalus ; skull from the lateral, superior, and 

 palatal aspects, one-sixth nat. size. L. Jurassic (L. Lias); Lyine Regis, 

 Dorsetshire, ag., angular; art., articular; b.occ., basioccipital ; b.s., basi- 

 sphenoid; d, dentary; ecpt., ectopterygoid ; fr., frontal; i.pt., interpterygoid 

 vacuity; j, jugal; mx., maxilla; nar., external narial opening; orb., orbit; 

 pa., parietal; pas., parasphenoid ; pin., pineal foramen; pi., palatine; 

 pmx., premaxilla; prf., prefrontal ; pt., pterygoid; pt.nar., posterior nares; 

 ptf., postfrontal; pto., postorbital; q.j., quadrato- jugal ; qu., quadrate; s, 

 supratemporal vacuity; s.ag., surangular; s.o., suborbital vacuity; s.t., 

 supratemporal (prosquamosal) ; sq., squamosal ; v, vomer. (Slightly 

 modified after C. W. Andrews.) 



D. Plesiosaurus dolichodirus; cervical vertebra, left lateral aspect, one-quarter 

 nat. size. L. Lias; Lyme Regis, r, rib. 



E. Cryptoclidus oxoniensis; transverse section of abdominal region, about one- 

 tenth nat. size. U. Jurassic (Oxford Clay) ; Peterborough, abd., abdo- 

 minal ribs; r, rib. (From immature specimen shown in the photograph, 

 fig. 107.) 



F. Plesiosaurus dolichodirus; caudal vertebra, anterior end-view, one-quarter 

 nat. size. L. Lias; Lyme Regis, ch., chevron bone; r, rib. 



G 1 , G J . Murcenosaurus leedsi; pelvis from the superior and left lateral aspects, 

 one-fourteenth nat. size. Oxford Clay; Peterborough, fe., femur; il., 

 ilium; is., ischium; pb., pubis. (After C. W. Andrews.) 



H, I. Plesiosaurus dolichodirus; pectoral (H) and pelvic (I) paddles of same 

 individual, one-twelfth nat. size. L. Lias; Lyme Regis, fe., femur ; fi., 

 fibula; h, humerus; /. intermedium; r, radius; t, tibia; u, ulna; x, pisi- 

 form bone. (British Museum, no. R. 1756.) 



J. Plesiosaurian propodial bone (huraerus or femur), in median longitudinal 

 section, one-fourteenth nat. size. U. Jurassic (Kimmeridge Clay); Ely. c, 

 central cavity; ep., epiphyses ; s, shaft: (British Museum, no. R. 1381.) 



