CHELONIA. 33 



recent skull) between the palatines, prefrontals, and maxillaries ; the anterior border 

 of the temporal fossa, formed by the malar and pterygoid, is entire on one side, and 

 shows that that vacuity was as broad as it is long. The olfactory excavations in the 

 maxillaries are deep. The articular surface of the tympanitic pedicles closely accords 

 with those of recent Chelones. The very regular triangular form of the skull indicated 

 by this fragment, has induced me to propose the name of Chelone trigoniceps for the 

 species. 



Chelone cuneiceps. Owen. Tab. XV. 



One of the most complete and instructive crania of the fossil turtles of our Eocene 

 deposits is the subject of T. XV, the opportunity of describing and figuring which has 

 been kindly afforded me by J. Toulmin Smith, Esq., F.G.S., of whose cabinet it forms 

 part, and by whose skilful manipulation its variously configurated exterior has been 

 disencumbered of the hard adherent clay. 



From the Chelone breviceps this specimen differs by its more prolonged and pointed 

 muzzle ; by the more sudden and sloping declivity of the prefrontal part of the 

 cranium (fig. 1, 14) ; by the minor degree of rugosity of the surface of the bones ; and 

 by the different disposition of the superincumbent horny scutella, which is indicated 

 by their impressions. In the general arrangement of these impressions it accords 

 better with the cranium of the Chelone longiceps ; but differs in the greater breadth 

 of the skull as compared with its length ; in the minor extent of the bony palate 

 (fig. 3, 20, 21), the more advanced position of the posterior nostrils, and the greater 

 length of the pterygoids (24). From the Chelone convexa it differs, in the greater 

 relative breadth and flatness of the frontal bones, and of the whole interorbital 

 platform (fig. 2, 11), in the downward slope of that part of the cranial profile, and in 

 the more prominent convexities of the palatal processes of the maxillaries. From the 

 Chelone planimentum it differs also, by the broader prefrontal part of the interorbital 

 space, as compared with the transverse diameter of the back part of the skull ; by 

 the minor degree in which the frontal enters into the formation of the upper rim of 

 the orbits ; by the minor depth of the suborbital part of the maxillary and malar 

 bones, and by a very different arrangement of the supracranial horny scutella. 



The basi-occipital (T. XV, figs. 3 and 4) is remarkable for the strong development 

 of the tubercles for the insertion of the strong " recti capitis antici," and for the depth 

 of the median groove between them ; the semicircular fossa in front of these processes 

 is bounded by a well-developed basi-sphenoidal ridge (5), the curve of which is deeper 

 than in Chel. longiceps, but shallower than in Chel. breviceps. In the Chel. caouanna, in 

 which the basi-occipital tuberosities are better developed than in the Chel. imbricata 

 or Chel. myclas, they are bounded anteriorly by an angular or chevron-shaped ridge of 

 the basi-sphenoid. The exoccipitals (2) form the usual share of the trilobate occipital 



5 



