192 G. E. Wieland — Upper Cretaceous Turtles. 



Adocus, Osteopygis, Lytoloma, and Chelone thus virtually 

 form a series passing from a strong cleido- to a weak dactylo- 

 sternal plastral junction. The large anterior and posterior 

 plastral foramina and the elongated entoplastron, however, are 

 distinct departures from such a plastron as that of Adocus, lead- 

 ing to the plastral form seen in living sea turtles. 



Synopsis of the Characters of Lytoloma. 



Cranium. — Agreeing in most characters with the existing 

 Cheloninse, but specialized for a conchifragous habit ; short, 

 very broad, with external nares directed as much upward as 

 forward. Vomer large and heavy ; internal nares roofed over 

 back of vomer by union of palatines in Eocene species (Lydek- 

 ker and Dollo), but probably not in New Jersey Upper Creta- 

 ceous forms; palatal surface perforate for lower jaw in L. 

 {Euclastes) platyops Cope, heavy and imperforate in Lytoloma 

 (Yale specimen No. 913a = L. angustaf). 



Lower Jaiv. — Short and broad, with a very long symphysis, 

 and wide and deep lateral pits for the attachment of heavy 

 masseters. 



Carapace. — Suborbicular in outline, with wide and persistent 

 pleuro-marginal fontanelles; composed of 51 bony plates with 

 the boundaries of the (38) horn-shields distinct, the numerical 

 agreement thus being complete in Osteopygis, Propleura, and 

 Chelone. Marginals 11 pairs, narrow anteriorly, but increasing 

 in breadth to the eleventh, which is nearly as broad as long, 

 with outer borders forming an evenly continuous curve to the 

 eighth marginal, beyond which the carapace is more and more 

 emarginate at the ends of the marginals, upper and nether sur- 

 faces of equal area, inner surface a shallow rounded furrow ; 

 both outer surfaces of fourth marginal nearly flat, with slight 

 concavity of the upper surface and convexity of the lower sur- 

 face beginning with the fifth and increasing to the eleventh, 

 supported by rib tips only, and upper inner borders bounding 

 the series of large pleuro-marginal fontanelles; rib pits deep 

 and of round to elliptical section, those for the second to the 

 eighth ribs being borne posteriorly on the third to ninth mar- 

 ginals inclusive, the tenth marginal ribless and the eleventh sup- 

 porting the ninth rib anteriorly, as in Chelone. Nuchal large 

 and broad. Neuralia (9) without marked tendency to the sup- 

 pression of any of the final members of the series, as in Adocus 

 and Osteopygis. Antero- and postero-pygal as in Chelone; 

 surface of the j)lates smooth, not pitted, and as in the living 

 Chelonians. 



Horn-shields.— (38 in number) agreeing numerically with 

 those of Chelone. Yertebralia broader than long. 



Plastron. — Much as in Osteopygis, but with a narrower 



