176 DE. A. S. WOODWARD ON EXTINCT [Mar. 5, 



me that the relative development of the mandibular beak varies 

 considerably in the Cryptodiran genus Ohelone andin the Pleurodirau 

 genus Sternotlicerus, Avhile some species of Podocnemis have two 

 marginal palatal ridges, others have only one. I therefore conclude 

 that there is not yet sufficient reason to separate the South 

 American species now made known from the genus Miolania, 

 hitherto discovered only in the Australian region. It must be 

 regarded merely as forming a very distinct species, characterized 

 by the much-depressed form of the cranium, the enormous size of 

 the occipital crest, the triangular shape of the postero-lateral 

 " horns," the simple rounded ridge on the palate, and the total 

 absence of an internasal septum. It may be appropriately named, 

 following Ameghino, Miolania argentina. 



It will also be observed that Mr. Boulenger's determination of 

 the Pleurodirau nature of the genus Miolania ^ is now completely 

 established. 



II. An Extinct Ophidian, Diniltsia fatagonica, gen. et 

 sp. nov. (Plate XX,) 



Mr. Eoth's discovery of a fossil Ophidian in the red sandstone 

 of Neuquen, associated with typical Mesosuchian Crocodiles, has 

 already been recorded ■ ; but the unique specimen referred to has 

 not hitherto been studied. It comprises the greater part of the 

 skull and mandible, and fragmentary remains of the anterior half 

 of the vertebral column ; the cranium being in an especially good 

 state of preservation. 



The skull (Plate XX. figs. 1,1a) is long, narrow, and depressed, 

 with the cranial region as long as the facial region. It seems to have 

 been widest at the occiput, where the otic region is very massive ; 

 and the maximum compression is immediately in front of this, where 

 the parietals rise into a prominent sagittal crest. The constitution 

 of the hinder part of the skull is best seen on the left side of the 

 fossil, where there is only one slight antero-posterior crack {x) in 

 the bones. The right postero-lateral angle, on the other hand, is 

 fractured and displaced downwards. The foramen magnum, 

 which is filled with matrix, is completed above by the exoccipitals 

 (ecc.occ), which meet in the middle line. They are directly con- 

 tinuous on each side with a great, expanded piece of bone (op.), 

 which curves backwards as well as outwards and abuts upon the 

 bone at the upper end of the quadrate. This expansion of the 

 exoccipital is probably the opisthotic, which is similarly fused with 

 the exoccipital in Lacertilia and the extinct Mosasaurs. Above 

 the exoccipitals is the short but laterally-extended supraoccipital 

 (s.occ), which completes the sagittal crest behind. Its lateral 

 extremity on the left is in contact with a small trace of bone (o.), 



^ G. A. Boulenger, " On the Systematic Position of the Genus Miolania, 

 Owen {^Ceratochelys, Hvxxley)," P. Z. S. 1887, pp. 554, 555. Also "Eemarks in 

 reply to Dr. Baur's Article on the Systematic Position of Miolania," Ann. Mag. 

 Nat. Hist. [6] vol. iii. 1889, pp. 138-141. 



2 A. Smitli Woodward, Auales Mus. La Plata — Paleont. Argent, no. iv. 

 (1896), p. 1. 



