MORPHOLOGICAL REVISION OF THE SUBORDER. 139 



A cleithrum occurs in No. 4060 Am. Mus. ; as suggested by the occurrence in 

 C. iiatalis, it is a slender, almost rudimentary element, articulating with the end of 

 clavicle and upper (anterior) edge of the scapula. 



The scapula, No. 4146 Am. Mus., is larger than, but very similar to, Dimetrodoti 

 incisivus. (Plate 30, fig. 2.) 



The humerus is of the form of Dii>ietrodon gigas ; it is proportionately longer and 

 more rugose. (Plate 31, fig. 2.) 



The anterior portion of the limb and the foot are unknown. 



The pelvis is described in the discussion of Naosaunts claviger. 



Abdominal ribs : In preparing the specimen of A'', daidger for mounting. Dr. 

 Matthew found traces of abdominal ribs, showing their presence in this animal. 



The posterior limb is unknown. Many isolated limb bones may belong to this 

 genus, but they can not be definitely determined. 



There are several enormous terminal phalanges with the spines, which indicate 

 that the feet were armed with powerful claws ; this animal probably greatly exceeded 

 the genus Dimetrodon in the development of the claws. (Plate 30, fig. 3.) 



Naosaurus claviger Cope (p. 59; plates 28, 29, and 35). 



Characteristic specimens: No. 4002 Am. Mus. : The type. No. 4036 Am. Mus. 

 Nat. Hist., Cope, coll. : The posterior half of a skull. No. 4015 Am. Mus. Nat. Hist, 

 Cope, coll. : A vertebral column with cervicals and dorsals in fair condition, but the 

 spines incomplete and several others in a refractor}^ concretionary matrix. No. 4103 

 Am. Mus. Nat. Hist., Cope, coll.: An interclavicle and scapulse. No. 4146 Am. Mus. 

 Nat. Hist., Cope, coll.: A scapula of the left side. 



The skull : In 1888 (70) Cope published a pretty full description of this species, 

 evidently founded on specimens No. 4036 and No. 4002 Am. Mus. This description 

 is accompanied by figures of the spines and the interclavicle. 



"The skull (No. 4036 Am. Mus.) : One of the best-preserved specimens of N. 

 claviger includes a skull, but the extremity of the muzzle is unfortunately wanting. 

 The median line rises forwards so that the convexity of the top of the muzzle is higher 

 than the posterior parts of the skull, whose profile descends rapidly. This throws 

 the orbit far back and gives the animal a peculiar appearance. 



"The orbit is nearly round, the superciliary border being arched. Anterior to it 

 is a large antorbital fossa boiinded by a longitudinal ridge above. Above the ridge 

 is a longitudinal groove, which is separated from that of the opposite side by a narrow 

 ridge only. The quadrate bone is large and laminiform, and is truncate above, having 

 a good deal the shape of the same bone in a fish. The parietal buttress is produced 

 downwards and backwards, and is in contact with the superior third of its posterior 

 border. Beneath and within it is a narrow opisthotic. The pterygoid is large, and 

 is distally vertically compressed. Anteriorly it becomes flattened so that it is hori- 

 zontal, and is studded with small conical teeth rather distantly placed. * * * * 



" I'ertebra (No. 4002 Am. Mus.): A large series of these are preserved, and they 

 show many interesting characters. The intercentra are not distinct in the anterior 

 part of the column, are separated posteriorly and in the sacrum. The centra are com- 

 pressed and have an acute inferior keel. The neural spines are moderately compressed 

 below the first transverse process ; above this point they are antero-posteriorly oval in 

 section. The distal half is compressed. They expand to a point below the apex, 

 where the anterior edge extends obliquely backwards to the summit. A short corre- 

 sponding oblique edge truncates the posterior superior angle. The medullary cavity 



