642 s. ^y. williston 



symphysis. Acetabulum imperforate, formed by all three bones; 

 pubis, ischium and ilium more or less fused in adult. 



Humerus expanded at its two ends into more or less divergent 

 planes; an entepicondylar foramen present; olecranon more or 

 less produced; radiale, intermedium, ulnare, centrale, and four 

 distalia always ossified, a second centrale and the fifth distale 

 rarely unossified; pisiform usually (perhaps always) present. 

 Two bones in proximal row of tarsus (calcaneum and astragalus), 

 at least one free centrale (rarely unossified) and five distalia. 

 Manus and pes pentadactylate, the phalangeal formula 2, 3, 4, 

 5, 3-4; a vacuity for the mesopodial perforating artery in both 

 carpus and tarsus (Limnoscelis?, Diasparactus?). 



INCONSTANT OR VARIABLE CHARACTERS 



Skull smooth or rugose, with two, one, or no temporal perfora- 

 tions on each side; rarely with spiny protuberances; postparietal, 

 tabulare and supratemporal inconstant, primarily with all known 

 membrane bones of the Stegocephalia; lacrimal usually extend- 

 ing to nares; transpalatine not yet demonstrated, quite surely 

 absent in some forms; no posterior palatine vacuity hitherto 

 observed; basisphenoid suturally or loosely articulated with 

 pterygoids.'* Teeth usually thecodont, rarely acrodont, usually 

 attached to vomers (prevomers), rarely to splenials. Occipital 

 condyle convex, flat or concave distally. 



From two to six or seven cervical vertebrae; twenty-three 

 to at least twenty-seven presacral ; one to three sacrals ; and from 

 about twenty-five to more than fifty caudals. 



Articulation of ribs either continuous from capitulum to tuber- 

 culum, or separated by a distinct neck; that is, the ribs are 

 either single-headed or double-headed. Spines of thoracic verte- 

 brae rudimentary, or short, or moderately elongated, or greatly 

 elongated. Ventral ribs present or absent. 



■* Incidentally I may remark here that Versliiys' recent identification (Zool. 

 Jahrb., 1912, 651) of the basisphenoid in the American pterodactyl Pteranodon 

 is indefensible. The basisphenoid invariably forms part of the brain capsule, 

 lodging the hypophysis. As Versliiys would identify the bone in Pteranodon it 

 is far removed from all relations with the brain-case or the cranial bones. Eaton, 

 I believe, is right in restricting the basioccipital to the extreme posterior part. 



