OSTEOLOGY OF THE AEMOKED DIN OSAUEIA. 115 



Another plate, probably from the dorsal series, is much more compressed than either of the two 

 already noted, and seen in profile has the form of a rather narrow high triangle. 



None of the large flattened plates so characteristic of Stegosaurs hitherto described are present, 

 and while the material available is too scanty to warrant any positive assertion regarding them, yet it 

 seems probable that in the species under consideration all the plates were small and heavy. 



The nuchal armor consists of small, thick, irregularly quadrilateral plates slightly keeled, and 

 these, save for their smoothness, are suggestive of the nuchal and dorsal plates of crocodiles. 



The throat was protected by rounded ossicles varying from 3 to 25 mm. in diameter, and many of 

 these are present on the slab containing the nuchal plates. It is entirely probable that this species 

 represents a distinct genus of Stegosaurs; but in the absence of material on which to base a generic 

 diagnosis it seems best not to bestow upon it a new generic name. 



This specimen was recognized by the late Prof. O. C. Marsh as representing a new form, and as it 

 was almost the last specimen to be studied by him it seems particularly appropriate to name the species 

 in honor of one who did so much to make the Stegosaurs known. 



The following are the measurements of the spine and plates described: Caudal spine, shown on 

 plate 20, 370 mm. high and 252 in antero-posterior diameter; caudal plate, shown on plate 21, 304 mm. 

 high and 155 in antero-posterior diameter; width of articular face 148 mm.; dorsal plate 380 mm. in 

 greatest height, and 198 in antero-posterior diameter. 



Scapula and coracoid. — The scapula as in Anleylosaurus is especially thick and 

 massive. Thickest above the humeral articulation and narrowest just posterior 

 to that point, where it measures 10S mm. across the shaft. 



The upper portion of the blade is missing, but from the proximal portion it 

 would appear to have been decidedly concave from end to end on the inner sur- 

 face. A heavy oblique ridge rises from the median external surface of the shaft 

 just posterior to the glenoid cavity and continues forward and upward, terminating 

 at the acrominal border. The forward termination of this ridge overhangs the 

 lower external surface of the bone. It appears very similar to the outwardly 

 curved superior borders of this portion of the Arikylosaurus scapula as described 

 by Brown, 1 and resembles somewhat the process found on the scapula of Hylae- 

 osaurus. 2 



The coracoid is firmly coossified with the scapula and with it forms a shaliow 

 but extensive glenoid cavity. The coracoid foramen passes almost straight through 

 the bone, not diagonally as in Stegosaurus and Anhylosaurus. The coracoid is a 

 flattened discoid bone, its general proportions being well shown in plate 26, figure 3. 

 At the articulation with tbe scapula it has a vertical measurement of 190 mm. 



Humerus. — The humerus of Ho-plitosaurus is represented by the distal half of 

 the right and the proximal portion of the left (pi. 26, figs. 1 and 2) . These pieces show 

 it to have been a sh ort bone, with widely expanded ends, that are much flattened ante- 

 roposteriorly. The deltoid ridge, although broken, appears to have been well devel- 

 oped, and as in Stegosaurus extended well down on the side of the shaft. The 

 radial and ulnar condyles are feebly developed, being separated by a very shallow 

 trochlear depression. 



The supinator ridge is much more prominent than in Stegosaurus, and its great 

 transverse development adds much to the width of the distal end of the bone. 

 On the posterior side the olecranon fossa of the mammalian humerus is represented 

 by a broad and very shallow depression. The head is less robust than in Stegosaurus 

 and does not overhang to any appreciable extent the posterior surface of the shaft. 



' Bull. Amer. Mus. Nat. History, vol. 24, 1908, p. 196. 



2 Owen, Wealden, and Purbeck Reptilia, Mon. Pal. Soc, 1S58, pt. 3, pi. 4. 



