EUCHELYS MACROPUS. 449 



Descr. — The snout is quite compressed, the superior region of 

 the upper jaw, immediately in advance of the nostrils, exhibiting a 

 subacute process which seems to occur in most Ghelonidae during the 

 early stages of their growth. The anterior aspect of the upper jaw 

 is shelving inwardly downwards, a trait which is gradually obliterated 

 as the animal grows older. 



The middle occipital plate is proportionally very large, heptagonal, 

 narrowest anteriorly, the odd angle, which is contiguous to the vertex 

 plate, being the smallest. The vertex plate itself is small, pentagonal, 

 anteriorly acute, engaging between thefrontals, which are six-sided and 

 very much elongated. The parietals, which are next to the middle 

 occipital in size, are subrounded and obscurely heptagonal, presenting 

 a broad side to the middle occipital ; two small sides : one to the vertex 

 plate, another to the frontals ; two others, equally small : one to the 

 anterior latero-occipitals, another to the upper postorbitals ; whilst the 

 remaining two sides constitute, together with the frontals, the superior 

 rim of the orbits. The latero-occipitals are obscurely six-sided, the 

 anterior pair being somewhat larger than the posterior pair. The 

 postoccipitals are transversely elongated, contiguous upon the middle 

 line of the occiput, meeting sideways both latero-occipitals. The irife- 

 rior postorbital is always larger than the three remaining ones, which 

 are either subequal, else, the uppermost or first is the smallest, and 

 the second occasionally larger than the first and third, which in that 

 case are subequal. The temporal shields, or plates, are, as usual, 

 smaller over the tympanum than at its periphery. The extremity of 

 the lower jaw is curved upwards as in Thalassochehjs. An elongated 

 infra maxillary shield may be observed, followed by three or four quite 

 small plates, beneath the angle of the mouth. The mental shields are 

 but three in number, transversely arranged over the chin. The gular 

 region, throat, and neck exhibit numerous, small, plate-like, dermic 

 indurations, similar to those which may be seen about the axillar and 

 inguinal regions. 



Viewed from above, the carapax is regularly cordiform ; the verte- 

 bral ridge is very obtuse, and the costal ridges very obsolete; its peri- 

 phery is but very slightly emarginated at the commissure of the mar- 

 ginal shields. Its entire surface is minutely pitted, assuming a some- 

 what reticulated appearance. The second and third vertebral shields 

 are more developed, transversely, than any of the others, and more 

 regularly hexagonal also, than the first and fifth; the fourth is penta- 



113 



