FAUNA OF THE GOSATJ FORMATION. 



651 



with the skin. On the broad side this bony base is 1-^ inch thick : 

 on the narrow side the greatest thickness is inch. The horn- 

 like spine is placed obliquely upon it, and rises vertically, curving a 

 little backward or outward. It is ok inches high. Its base is ra- 

 ther more than 2| inches long, and 2y 1 inches wide. The spine is 

 slightly flattened on the convex and concave sides. The right 

 and left sides are nearly straight. The bone is covered with close- 

 set irregular vascular perforations similar to those on a horn-core. 

 (See Biinzel, pi. v. fig. 10.) 



Two other plates of quite as remarkable character are dissimilar in 

 form, one being twice the width of the other : but both had smooth 

 bases for attachment to the skin. The base is rounded at its lateral 

 margins, as though it were a bone distinct from the extraordinary der- 

 mal ornament which rises from it. The larger specimen (PI. XXVIII. 

 fig. 2) is 8 inches long and imperfect at one end. The articular base 

 appears to have been about 4^ inches long and 2 inches wide, while 

 the greatest width of the plate is 3^ inches towards each end of the 

 articular space, and in the intermediate area it becomes contracted 

 to about 2\ inches. The spine which existed at the other end of this 

 contracted area has been almost entirely broken away ; so that the 

 plate was originally probably a central oblong mass with constricted 

 sides terminating at each end in a large triangular spine, which was 

 directed upward from the body of the plate. The one spine which 

 is preserved is on its upper surface about 4 inches long, and at 

 the base 3| inches wide. It is slightly convex from side to side, 

 and terminates in a sharp cutting-edge on each side, which is lon- 

 ger and more convex on one side than on the other ; and the longer 

 edge is reflected a little upward. There are a few longitudinal sub- 

 parallel vascular grooves in the middle of this part of the plate. On 

 the under surface of this region the bone is' flattened on the two 

 sides, which converge towards a rounded ridge in the middle line, 

 which helps to give strength to the sharp dagger-like extremity in 

 which the bone terminates. The greatest thickness of this part 

 of the plate in the middle is ^ inch. Its base terminates 

 abruptly, perhaps owing to some crushing on the underside. The 

 middle oblong portion of the plate is studded over with conical tu- 

 bercles, the bases of which are pretty clearly defined, and the cones 

 are low, They are arranged across the bone in three rows with 

 four low conical tubercles in each of the two outer rows and 

 two larger tubercles in the middle, 1 inch in diameter, with three 

 on the external margin of each, making in all 6 in the middle. 

 These tubercles make an elevated border abutting against the tri- 

 angular spine. Their surfaces are roughened with close-set irre- 

 gular vascular punctures. The smaller plate (PL XXVIII. fig. 3), 

 of similar character, is rather better preserved, its total length 

 6 \ inches, length of the articular base 5|- inches. It carries a 

 vertically elevated spine, and the base beneath this is deeply con- 

 cave. The margins of the base are smooth and well rounded as 

 already described in the larger specimen. The width of the base 

 is 1-r^- inch. At one end the compressed spine rises at an angle 



