ICHTHYOPTERYGIA. 3 



Carnivorous Marine Reptiles with a Cetacean-like body (fig. 1), 

 devoid of exoskeleton, and with the limbs modified into paddles, in 

 which the proximal (propodial) segment is very short; the pha- 

 langeals are ovoid or polygonal, and articulate together to form a 

 kind of pavement, the number in each digit being increased beyond 

 the normal, and frequently additional digits are developed. Skull 



Fig. 2. 



Ichthyosaurus intermedius. — Left lateral view of skull ; from the Lower Lias of 

 Lyme-Regis. Reduced. Pmx, premaxilla ; Mx, maxilla ; N, nares ; La, 

 lachrymal; Prf, prefrontal; Fr, frontal; Pa, parietal; Pt, postfrontal ; 

 St, supratemporal ; Sg, squamosal; Qj, quadratojugal ; Qu, quadrate; 

 Ju, jugal; PtO, postorbital. (After Huxley.) 



(fig. 2) large, with an elongated rostrum principally constituted in the 

 cranium by the premaxilla ; nares approximated to the large orbit, 

 in which the sclerotic has an ossified ring ; a parietal foramen ; 

 postorbital distinct from postfrontal, and lachrymal from prefrontal ; 

 frontal minute ; quadrate fixed, not fused with pterygoid, and 

 separated from middle of quadratojugal by a foramen ; a columella 

 (epipterygoid) ; a distinct opisthotic ; two temporal arcades, con- 

 nected together by the supratemporal l , which roofs over the 

 infratemporal fossa. Teeth confined to the jaws, implanted in a 

 groove, without anchylosis ; the crowns usually cylindrical and 

 fluted, but occasionally compressed, carinated, and smooth. Ver- 

 tebrae (fig. 3) primarily divisible into a precaudal and caudal series 

 without any differentiated sacrum ; centra very short and amphi- 

 ccelous ; precaudals (fig. 3) with an upper and a lower costal 

 tubercle on the centrum 2 ; caudals with a single tubercle ; neural 



1 In the nomenclature of this bone the usual determination is followed. 

 Baur, however (Anat. Anzeig. vol. i. p. 348, 1886, and vol, ii. p. 657, 1887 ; see 

 also Amer. Nat. vol. xxi. p. 838, 1887), reverses the names of the two bones 

 here termed supratemporal and squamosal. The bone here termed supratem- 

 poral is the prosquamosal of Owen, and the supraquadrate of Seeley ; and 

 is identified by Baur with the squamosal. 



2 In the first few vertebrae the upper tubercle may be partly or entirely on 

 the arch. 



b2 



