IN THE REPTILIA. 17 



II. The Mesozoic Reptilta. 



We may now examine how far the cranial types above described continued into 

 Mesozoic time, and ascertain whether any new forms appeared. 



In the first place, Abtosauelts Fraas presents a single foramen perforating an 

 otherwise continuous roof of the temporal fossa. This foramen is bounded below by 

 the postorbital and supratemporal bones. The postfrontal bone is closely joined to 

 the parietal, and has no posterior extension except to the postorbital. The zygomatic 

 arch is present and is continuous with the supratemporal and postorbital bones, there 

 being no infratemporal foramen. These details are derived from Fraas' figures copied 

 by Zittel in his Handbuch der Paleontologie.* In this figure no distinct zygomatic 

 (quadratqjugal), or supraraastoid, is visible, but whether they are wanting or fused 

 with adjacent elements, examination of specimens will best show. This genus is made 

 the type of a suborder of Crocodilia by Baur (Pseudosuchia), but it appears to me 

 to be typical of a special order (PI. lY, Fig. 2). 



The genus Ichthtosaueus presents especial features. Here we have a zygo- 

 matic arch, and no infratemporal foramen. There is a superior foramen, however, 

 which is bounded below by the postfrontal bone in front, and the supramastoid be- 

 hind ; which are themselves in contact below with the postorbital and the supratem- 

 poral. This foramen I call the supramastoid. A iDaroccipital bone is present in this 

 genus,'but no intercalare. See my memoir of 1870 above referred to (PL Y, Fig. 1). 

 The DiN"OSAURiA may be represented by Diclonius, of which I have a complete 

 skull before me (PI. III). Here there are superior and inferior foramina which isolate 

 two arches, of which the inferior is the zygomatic. The superior arch consists of the 

 supramastoid bone posteriorly, and apparently the postfrontal anteriorly. The supra- 

 temporal, small in Ichthyosaurus, has now disappeared. There is a distinct paroc- 

 cipital lying scale-like on the exoccipital. In Diclonius the supramastoid is fused 

 with the parietal,f but in Iguanodon, according to Dollo, it is distinct. ^^ The fact 

 that the postfrontal and postorbital are not distinct from each other in the Dinosauria 

 with which I am acquainted, makes the determination of the character of the supe- 

 rior arch somewhat difficult. This is probably the case in Diclonius, and is so repre- 

 sented by Dollo in Iguanodon. In a fine cranium of the Laramie Lcelaps incras- 



* Page 644, Fig. 569. 



f Cope. Proceeds. Acad. Phila., 1883, p. 110, PI. V. In this description and plate the sutural lines supposed to 

 separate the postfrontal from the postorbital and "squamosal " are of doubtful existence in the specimen. 

 X Bulletin de Musee Royale d'Histoire Naturelle de Belgique, II, 1883, p. 235, PI. II. 

 A. P. S. — VOL. XVII. C. 



