THE BONES IN THE ENALIOSAUEIA. 327 



early dorsal ribs differ from those of Plesiosaurus in carrying an epi- 

 pleuron, though the superior process which gives the cervical rib its 

 hatchet-shape in Plesiosaurus may be regarded as an anchylosei 

 epipieuron. The abdominal ribs of Hatteria are like those of Ple- 

 siosaurus ; and in one species (for two species seem to me to be 

 typified by the abdominal ribs figured by Dr. Griinther) the median 

 ji\^-shaped bone is overlapped by a splice from a bone external to it. 

 In another species this splice is replaced by a joint, and the ex- 

 ternal piece has a squamous expansion on the middle of its ante- 

 rior and posterior margin, unlike any thing seen in Plesiosau- 

 rus. But, as in Plesiosaurus, other bones are introduced between 

 these elements, so as to make the abdominal ribs nearly twice as 

 many as tlie costal ribs. 



The pectoral girdle differs from that of Plesiosatirus in having a 

 sternum and clavicles. Between these the interclavicle is anchy- 

 losed. The coracoid differs in its great extension in front of the ace- 

 tabulum, in its small size, in its connexion with the sternum, in 

 its wide union with the scapula. And only by revolving the sca- 

 pulae forward till they meet in front and are in the same plane with 

 the coracoids, and at the same time causing them to grow distally 

 at the expense of the sternum so as to obliterate it, could the 

 rhynchocephalous pectoral arch be brought into harmony with 

 that of Plesiosaurus. 



The pelvis differs chiefly in its smaller size, in the ischium of 

 Hatteria having a prominent posterior tuberosity, in the small 

 size of the os pubis, which has not a reniform outline or a convex 

 anterior margin, and in the compression of the ilium. 



§ 7. TJie Ophidian Characters of Plesiosaurus. 



The points of resemblance between serpents and Plesiosaurs 

 are so trifling that they may be neglected. In Python there is a 

 parietal crest. A superorbital bone excludes the frontal from the 

 orbit; and a narrow nearly vertical postfrontal makes the boundary 

 of the orbit behind, as in Plesiosaurus. There are remarkable dif- 

 ferences in that the squamosal and quadrate bones are loose, and 

 that the bones of the face and palate are loose. The malar and 

 quadrate -jugal bones are absent, and the side of the quadrate 

 bone is naked ; the preraaxillary is minute, and the skull has no 

 extension anterior to the nares ; a considerable interval separates 

 orbit and narine ; and there is no temporal fossa ; the maxillary 

 bones are very long, and on their inside the pterygoids run par- 



LINN. JOV-RS. ZOOLOGY. VOL. XTl. 24 



