404 REPORT OP NATIONAL MUSEUM, 1898. 



Tympanum more or less distinct. Body depressed, without dorsal 

 crest; dorsal lepidosis heterogeneous. Head covered with small scales, 

 bordered posteriorly by osseous spines. A transverse gnlar fold. Dig- 

 its with keeled lamelhc inferiorly. Femoral pores. Tail short. Lateral 

 teeth subconical or indistinctly tricuspid; no pterygoid teeth. A large 

 sternal fontanelle. No abdominal ribs. 



This peculiar genus ranges over the Central, Pacific, and Souorau 

 districts of Nearctica, and the political State of Mexico. It represents 

 the extreme of the terrestrial habit in the Iguanidte, corresponding in 

 this respect to Phynocephalus and Moloch among tlie Agamidte. The 

 latter it resembles in the horny processes of the skull and hetero- 

 geneous pholidosis, flat and spinous scales being mixed. The body is 

 very flat, and this form can be increased at the will of the animal by 

 the extension or abduction of the ribs which extend the abdominal 

 border. In defense the muzzle is depressed and the horns elevated, as 

 in Mammalia with posterior horns ; the back is also arched. Some of 

 the species are said to eject a bloody fluid from the eyes at such a time, 

 but this I have not observed. In life their horns constitute their only 

 defense, as they possess no speed. They are, however, abundant in 

 the dry regions of the southwest, where enemies are few, and where 

 they can take refuge beneath the formidable spines of the Agaves aud 

 Yuccas, and the prickles of the Opuntias. They can not be an attract- 

 ive mouthful to snakes, and I once saw a dead rattlesnake with the 

 horns of a Phrynosoma which it had swallowed penetrating the neck 

 through the upper integument, one on each side of the vertebral col- 

 umn. In confinement Phrynosomas can seldom be induced to eat, and 

 they frequently lay eggs. 



Osteology. — The following account of the osteology is derived from the 

 skeletons of three species, P. douglassii, P. cornntnni, and P. coronattm. 

 The description applies equally to each of these species unless otherwise 

 stated : 



The i)remaxillary has a very short alveolar portion which does not 

 bound the nostrils below (or very little, P. coronatxm). It has a supe- 

 rior spine and concave palatal border. The nasals are distinct and are 

 excavated in front by the large narial openings. The frontal is single, 

 is much narrowed in front by the prefrontals, but extends transversely 

 posterior to the orbits, where it sends forward an acute process in the 

 superciliary angle. The prefrontal is large and extends posteriorly to 

 or beyond the middle of the supraorbital border. It sends posteriorly 

 an acute superciliary process, which meets that of the frontal from 

 behind, over the eye in P. cornutum; does not quite meet it in P. core 

 7iatum, and fails to meet it by a longer interval in P. douglassii. The 

 lachrymal is small and is not reached by the anterior angle of the jugal. 

 The parietal is broad and short, and the pineal foramen pierces it at 

 the coronal suture. Its lateral border is very little decurved to meet 

 the petrosal. 



