THE SUBCLASS PARAPSIDA 259 



reptiles. Somewhat doubtfully associated with those remains are 

 others of ichthyosaur-Hke bones that the describer provisionally as- 

 sociated with the Ichthyosauria, bearing possibly a like relation to 

 the known Ichthyosauria that Glohidens does to the typical Pytho- 

 nomorpha. 



Middle Triassic. Omphalosaurus Merriam, Nevada. Pessopteryx 

 Wiman, Spitzbergen. 



10. ORDER PROTOROSAURIA 



Quadrupedal, arboreal, terrestrial, or subaquatic reptiles one to six 

 feet in length, with a single, upper temporal opening between the 

 parietal and the temporal arch, the quadrate fixed. Ribs in part or 

 all single-headed, articulating with centra — a single coracoid, an 

 interclavicle, and clavicles. 



This order, as here limited, is a provisional one, including several 

 reptiles, some of them imperfectly known, which cannot be placed in 

 any other known order. Most of them have hitherto been classified 

 with the Rhynchocephalia, from which they are distinguished by the 

 absence of a lateral temporal opening, so far as known. Perhaps when 

 finally known they will be found to be incoherent. For the present 

 they may be defined as families. 



Family Araeoscelidae. Very slender, arboreal or leaping, hol- 

 low-boned reptiles of less than eighteen inches in length, with long 

 legs and long tail. The broad lateral temporal region is formed ap- 

 parently of a single bone, here identified as the squamosal, the quad- 

 ratojugal absent. The dermosupraoccipital is apparently large. Lac- 

 rimal vestigial or absent. A parietal foramen. All cranial bones 

 paired. Palatal bones with teeth. At least seven cervical verte- 

 brae, twenty dorsal, two sacral, and a long, slender tail. Vertebrae 

 amphicoelous with persistent intercentra. Cervical ribs, at least, 

 single-headed, the dorsal more or less dichocephalous. Coracoid 

 and scapula closely fused. Humerus with both entepicondylar 

 and ectepicondylar foramina. Pelvis primitive. Phalangeal formula 

 primitive. Calcaneum produced. 



Araeoscelis, the type of the family, is the earHest definitely known 

 reptile with a single, upper temporal vacuity, bounded as in the 

 lizards, and a fixed quadrate. It was a very slender, leaping or 



