Ichthyosauria. 



33 



and a caudal series without any differentiated sacrum, the pre- 

 caudals have an upper and a lower costal or rib-tubercle on 

 the centrum ; the caudals have a single tubercle ; the neural 

 arches are attached by synchondrosis (by cartilage or gristle) to 

 the flat surfaces on the centra. Intercentra are present between 

 the skull and atlas, the atlas and axis, and the axis and the third 

 vertebrte. The precaudal ribs are double-headed. Ribs are 

 present in the caudal region ; the chevrons are not united below. 

 Abdominal ribs are present, but there is no sternum. There are 

 clavicles and a T-shaped interclavicle present in the pectoral 

 girdle ; the coracoids do not overlap, there is no ossified pre- 



"Wall-case, 

 No. 14. 

 Table-cases 

 Nog. 4, 5. 



Fig. 41. — Left lateral aspect of skull of Ichthyosaurus latifrons (KGnig), from the 

 Lower Lias of Barrow-on-Soar, Leicestershire, i nat. size. 



coracoid. The pelvis is weak, the iliac bones are not connected 

 with the vertebrae, and there is an open obturator notch. The skull 

 has very large orbits, and the eyes were surrounded by a ring 

 of broad bony (sclerotic) plates. The jaws are elongated, and 

 armed with powerful teeth implanted in grooves. The hand and 

 foot are modified into fin-like organs, composed of short polygonal 



ang 



Fig. 42. — A, superior, and B, right lateral aspect of the skull of Ichthyosaurus setland- 

 icii.s (Seeley) from the Upper Lias of Normandy (reduced). Pmx, premaxilla; Mx, 

 maxilla; N, nares; Na, nasal; Fr, frontal; I'rf, prefrontal; Pf/, postfrontal ; Pa, 

 parietal; /, jugal; QnJ quadratojugal; Sq, squamosal; St, supratemporal ; Par, 

 postorbital ; A, orbit; S, supratemporal fossa; Sd, sclerotic; Md, mandible; d, 

 dentary ; op, splenial ; ang. angular ; k, articular (after Zittel), J nat. size. 



bones, arranged in five closely approximated rows, with super- 

 numerary rows of marginal ossicles added (see Figs. 45 and 46). 

 The largest entire Ichthyosaurus is from Lyme Regis, and 

 measures 22 feet in length and 8 feet across the expanded 

 paddles ; but detached heads and parts of skeletons prove that 

 they often attained a far larger size than this. 



(1876) 4 



