1892.] 205 [Cope. 



the anterior end, where it is elevated into a low anterior spine. Chevron 

 bones intercentral. Four sternal ribs and two from the xiphoid rod. 



Scapula very sliort, with a lai-ge superior proscapula. Coracoid with 

 two notches. Sternum wide and emargiuate posteriorly, spreading the 

 xiphoid rods far apart. No foutauelie. 



Pelvis with the pubis transverse and the pectineal process external. 

 Ischia rather slender, with a short symphysis, and each with a long tuber- 

 osity. 



This genus is remarkable for the combination of characters it displays. 

 The zygosphenal articulation allies it to Dipsosaurus and the larger Ig- 

 uanidaj, but the separated ceratobranchials, and the wide sternum are like 

 that of the Phrynosomas, with the exception of the fontauelles. The 

 transverse pubes have a similar significance. 



ScELOPORUS Wlegmann. 



As a basis for an examination of the osteology of this genus I have 

 before me two skeletons of the S. undulatm and one of the S. spinosus, 

 from the National Museum. 



The premaxillary bone has a long superior spine, and is truncate on the 

 palatal face, and has the button-like pr()cess. The nostrils are partially 

 vertical so that the nasals are a little shortened in front. The latter are 

 rather large and are distinct. The frontal is simple and narrow, and is 

 strongly grooved on the middle line below. The parietal is short and wide, 

 and is perforated by a large pineal foramen which touclies tlie coronal 

 suture. Parietoquadrate arch distinct. Supraoccipital broadly but loosely 

 attached, confluent with exoccipltals. Prefrontals large, not reaching 

 postfrontals above ; lachrymal small and joining jugal. Postfrontal a 

 small splint ; postorbital large, extensively in contact with jugal and supra - 

 temporal. Paroccipital small. Vomers short, divaricate and separated 

 by a deep notch behind. Palatine with the vomerine process longer than 

 the maxillary ; palatine foramen large. Palatines and pterygoids well 

 separated from each other on the middle line ; ectopterygoid deflected at 

 its internal extremity. Basipterygoids developed. Quadrate with two 

 conchs, the internal the narrower. Presphenoid rudimental ; sphenoid 

 and basioccipital coossified ; descending lateral processes of the latter 

 strongly developed. The supraforaminal part of the petrosil is very 

 short ; the infraforaminal portion is produced beyond it and is nearly hor- 

 izontal in position. The foramen nervi octavi is at the bottom of a fossa. 

 Epipterygoid resting on pterygoid much posterior to ectopterygoid and 

 reaching parietal without touching petrosal. Occipital condyle not sub- 

 divided by grooves. 



The hj^oid system includes a pair of well-separated short second cerato- 

 branchials, and rather long and slender first ceratobranchials and cerato- 

 hyals, which have no expansions. Hypobranchials moderate, supporting 

 ceratohyals at extremities. 



Mandible with Meckel's cartilage exposed at the distal part. Coronoid 



