NATURAL SCIENCES OP PHILADELPHIA. 225 



three series one toward the serpents by Amphisbfenia, one to the partially 

 degraded type of the Geccos, and lastly through the highest or acrodont se- 

 ries, to Chamaeleo on the one hand and Hatteria on the other. 



In the first case the prolonged development of the superior temporal is fol- 

 lowed by a decurving of the parietal border, the closer attachment of the occi- 

 pital sclerotome, and shortening of the squamosal and mastoid. Finally, the 

 temporal, with the pieces adjoining anteriorly, begin to restrict a foramen 

 ovale, the orbito-sphenoid is developed, and the articular and angular pieces 

 of the mandible are represented by but one piece : the columella disappears. 

 In the last direction, the temporal is not elongate, nor is there any tendency 

 toward a more complete closure of the cranial cavity. The inferior or ? pet- 

 rous wing of the temporal is directed inwards instead of forwards ; the parietal 

 fontanelle does not diminish, and the premaxillaryboneis seen to form a regu- 

 larly decreasing series. The mesosternum and columella diminish in length 

 and disappear, and the splenial appears smaller and smaller to extinction. 

 The subarticular strengthens the inner rather than the outer wall of the man- 

 dible, and the external direction of the coronoid is reversed. The type of 

 Hatteria doubles the premaxillary, and exhibits the vertebrae amphicoelian. 



In approaching the Geccos, the bones of the palate are seen to be thinner 

 and more expanded, and the articular piece of the mandible is lost. In the 

 full type the ossification is of the lightest description, and the fascial and 

 basement membranes often present incomplete deposits of bony tissue ; thus 

 the parietal and sternal fontanelles disappear. The parietals are not, as 

 usual, united, and there is a dimunition (in Uroplates nearly obliteration), 

 of the median or basilar segment of the occipital condyle. There is a temporal 

 ala peculiar to this suborder. 



The following is a synopsis of the prevailing characters of the suborders : * 



ACRODONTA. 



Shanks of teeth compressed, most always between two alveolar walls. 



Coronoid bone produced posteriorly, on outside of ramus. 



Articular present separate from angular. Splenial reduced, more frequently 



wanting. 

 Subarticular small on outer, much prolonged on inner face of ramus. 

 Groove from splenial to mental foramina not closed over Meckel's cartilage. 

 Premaxillary nearly always separated from vomer by maxillaries. 

 Pterygoids not touching body of sphenoid. 

 Frontal not arching over the olfactory lobes. 

 Parietal single, receiving the gomphosis of loosely attached occipital segment 



internally. 

 Temporal with longitudinal wing only ; superior plate not produced beyond 



the arched body. 

 Orbitosphenoid wanting. 

 Suspensoria two, arches complete. 

 Rhiptoglossa and Pachyglossa. 



NYCTISAURA. 

 Shanks of teeth cylindrical, attached to the inner side of an alveolar wall. 

 Coronoid bone produced anteriorly and posteriorly. 

 Articular wanting. 



Subarticular largely developed exteriorly, not interiorly. 

 Splenial elongate ; Meckel's cartilage covered between the splenial and mental 



foramina. 

 Premaxillary broad, in contact with vomer. 



* Not a few of the characters here noted are pointed out in special cases in Stannius' most ex- 

 cellent Zootomie der Amphibien. 



1864.] 15 



