Maryland Geological Survey 185 



The articulation is a smooth, cylindrical concavity with no trace of ridges 

 to limit lateral motion. It is probable that it was formerly somewhat 

 cup-like, as the preparator has slightly altered the shape of the bone. 

 The articular end is full of a cancellous tissue, nevertheless there was 

 a well-defined medullary cavity in the shaft. The portion preserved 

 measures in height, 73 mm.; in width, 58 mm. 



The first phalanx of the third digit (No. 2521, G. C.) (fig. 2) is 

 entire, most excellently preserved, and presents a decided similarity to 

 the type of AUosaurus fragilis; differing therefrom in being more de- 

 pressed proximally, especially in the broader, flatter under surface. 

 Distally, the present type is not so broad relatively as that of A. fragilis, 

 and the articular face is more concave transversely. Altogether the two 

 bones are quite distinct in conformation. 



DIMENSIONS 



Length 110.0 mm. 



Transverse diameter distal face 55.0 mm. 



Vertical diameter distal face 35.5 mm. 



Transverse diameter proximal face 70.5 mm. 



Vertical diameter proximal face 50.0 mm. 



Least transverse diameter, shaft 41.0 mm. 



There are also two distal caudals, one ISTo. 5701, the other un- 

 numbered, both of the TJ. S. National Museum collection, each character- 

 ized by a flattened ventral aspect and the development of a slight keel 

 along the sides, giving it a somewhat hexagonal section. The neural 

 spine is reduced to a low ridge fading out posteriorly, while the zygapo- 

 physes are much prolonged. 



Length of centrum of No. 5701 68.7 mm. 



Length of centrum of unnumbered specimen 67.5 mm. 



The latter is somewhat stouter and has a more decided upward arch. 



AUosaurus medius is a fairly well-defined species, though the only one 

 of the original cotypes referable to it, the tooth, is one of the least dis- 

 tinctive features of the skeleton. The remains which I have referred to 

 it, however, are all from the same locality and .formation, and are all 

 relatively about the same proportionate size, judging from the remains 

 of AUosaurus fragilis. 



