35 



M. 



Length of centrum of anterior caudal : . . : .053 



Depth of cup of anterior caudal .044 



Width of cup of anterior caudal 041 



Width of neural spine 033 



Elevation of neural spine, (apex lost) 070 



Diameter of centrum of twenty-fourth caudal, | tmnsver ^e 040 



Length of centrum of twenty-fourth caudal 042 



This species appears to have had proportions not unlike those of 

 Platecarpus coryphctus the specimen described being larger than that 

 on which the latter is based. It is also rather larger than the Cli- 

 dastes planifrons, the largest of its genus, but which, since its caudal 

 vertebrsB are unknown, may be found to be a Sironectes. It differs spe- 

 cifically from the S. anguUferus in the less development of the zygosphen, 

 especially on the anterior vertebrte, and its deep emarginations in front 

 where well developed. From its general characters I anticipate that the 

 quadrate bone of this species will prove to be more like that of the 

 Platecarpi; that of C. plam/rons is that of the genus to which I have 

 referred it. 



PLATECAEPUS, Cope. 



Extinct Batrachia andEeptilia X. Am., 1869, pp. 185, 199. Proceed- 

 ings Academy Philadelphia 1872, p. 141 ; Holcodus^ Copei neo Gibbsii, 

 Proceed. Amer. Philos. Soc. 1871, December; Lestosaurus, Marsh, 

 Amer. Journ. Sci. Arts, 1872, June (Separata, p. 9). 



Besides the characters assigned to this genus in the analytic table 

 already given, Flatecarpus is characterized by the form of its teeth, 

 which are neither compressed, as in Liodon, nor broadly angularly 

 faceted, as in Mosasaurus (and Holcodus, fide Marsh), but are curved 

 and with subcylindric section. The exposure of the roots of the pala- 

 tine teeth is largely less or scarcely greater on the outer than on the 

 inner side. The caudal vertebme of the type-species, P. tympaniticus^ are 

 unknown ; but the quadrate bone and form of palatine teeth are quite 

 similar to those of the other species already referred to it. 



The species P. mudgei and P. tectiilus resemble each other in the form 

 of their quadrate bone, and are referred to this genus provisionally only. 

 The P. simus, Marsh, resembles the P. crassartus, Cope, but appears to 

 differ in the more depressed articular faces of the dorsal vertebrae. 



a. The stapedial pit inclosed between ridges : 



Platecarpus ictericus, Cope; Holcodus ictericus, Cope, Proceed. 

 Amer.Philo8ophicalSocietyl870, 577, and 1871, December; Lestosaurus 

 ictericus, Marsh, Amer. Journ. Sci. Arts, 1872, June. 

 Niobrara chalk of the Smoky Hill Eiver. 



Plateoarpus coryph^us, Cope; Holcodus coryphceus, Cope, Pro- 

 ceed. Amer. Philos. Society, 1871, December; Lestosaurus coryphceus, 

 Marsh, loc. cit. 



Niobrara chalk of the Smoky Hill Eiver. 



LATECARPTJS PELix, Marsh ; Lestosaurui 

 Sci. Arts, 1872, June, tab. xiii, fig. 4. 



Niobrara chalk of the Smoky Hill Eiver, Kansas. 



Platecarpus pelix, Marsh ; Lestosaurus felix, Marsh, Amer. Journ. 

 Sci. Arts, 1872, June, tab. xiii, fig. 4. 



