118 BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



Dermal armor. — As in Polacanthus, Hylseosaurus, AcanihopJiolis, Nodosaurus, 

 Stegopelta, Ankylosaurus, and Hierosaurus, the dermal arnaor of Hoplitosaurus 

 is of a complex character, combining as it does scutes of at least five different 

 forms; (1) simple flattened; (2) romided ossicle-like; (3) keeled; (4) triangular 

 plate-like, and (5) spined. 



(1) Those of the first kind are thin, rectangular scutes with rounded corners 

 and without surface sculpture or ornamentation. Two of these, shown in plate 27, 

 have the surface gently concave across the shortest diameter. 



(2) The ossicle-like scutes are the most numerous of those preserved. They 

 vary greatly in size and shape, being rounded, oblong, elHptical, and subrectangular 

 forms, that measure from 10 mna. to 50 mna. in the longest diameter. The block 

 of sandstone shown in plate 27 is thickly studded with them, in some instances 

 three and four being found one above another. 



These are undoubtedly the scutes to which Lucas refers as representing the 

 gular armature, a decision reached, no doubt, on account of the resemblance of 

 many of the scutes to ossicles forming the throat investiture of Stegosaurus. Since 

 the femur was found attached to the lower side of this block of sandstone, there 

 is reason for thinking that these ossicles in conjunction with other dermal struc- 

 tures may have formed a carapace-like covering over the pelvic region, as is known 

 to be the case in Polacanthus and Stegopelta} 



(3) There are numerous keeled scutes preserved, and they also vary much in 

 size and shape. Some are buttonhke, being raised in the center as a blimt cone- 

 like projection {d and d' , fig. 70), but the greater number are elongated, angu- 

 larly rounded, with a sharp keel on the dorsal surface, asymetrically placed. In 

 all of the examples before me this ridge is highest in the center, gradually sloping 

 toward both ends. None show a projecting spur such as found by Wieland ^ in 

 similar scutes of Hierosaurus. One of the better preserved measured through 

 the center has a thickness of 32 mm. One or more scutes are almost flat, with an 

 obtuse ridge (c and c', fig. 70), very similar to those found with the remains of 

 AcanthopTiolis, as described by Huxley.'' The ventral side of some of these scute 

 plates show the same texture of coarsely woven cloth, as described by Marsh in 

 Nodosaurus, and the dorsal surfaces of a few are scrobiculate as in Stegopelta.* 



(4) The large subtriangular, plate-like structures, closely resemble those of 

 Polacanthus, which Nopcsa ^ upon the evidence of associated material assigned 

 to the caudal region in two rows along the top of the tail (fig. 72) . Doubtless from 

 their close resemblance they will eventually be found to occupy a similar position 

 in Hoplitosaurus. The base is hollowed out as in the tail plates of Scelidosaurus 

 and Hylseosaurus, and as in the case in many of the dermal plates of Stegosaurus. 



A well-preserved example of this style gives the following measurements: 

 Greatest diameter antero-posterior, 210 mm.; greatest vertical diameter, 175 mm.; 

 greatest transverse diameter, 65 mm. As in nearly all the larger plates the lateral 

 surfaces are covered with blood-vessel impressions. 



1 S. W. WiUiston, Science (n. s.), vol. 22, 1906, p. 504. * R. L. Moodie, Science Bull., vol. 13, 1911, p. 267. 



3 Amer. Joum. Sci., vol. 27, 1909, p. 252. = Geol. Mag., vol. 2, 1905, pp. 246-249, flg. 6, pi. 12. 



3 Geol. Mag., vol. 4, 1S67, p. 65, pi. 5, flg. 1. 



