312 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 38. 



second marginal scutes and of the first vertebral and first costal. 

 The second peripherals arc both missing, but both third peripherals 

 are present. The length along the obtuse free border is 37 mm.; the 

 height, 33 nun.; thickness in front, 7 mm.; behind, 15 mm. As will 

 be seen (fig. 3) the marginal scutes run low down on this peripheral 

 also. One of the bridge peripherals, apparently the fourth, is 33 mm. 

 long and rises above the surface of the plastron 25 mm. Six of the 

 hinder peripherals are represented in the lot. The eighth has a 

 height of I") mm. The others have the upper border broken away. 

 Fig. I represents the anterior end of the eighth; fig. 5 a section of 

 probably the tenth. The free border of all these peripherals is sub- 

 acute. The position of the sulci on them has not been determined. 

 All the bones, where the outer surface is visible, present an orna- 

 mentation of pustules. They are flat topped and the intervening 

 valleys are very narrow. There are usually seven pustules in a line 

 5 mm. long. 



The fragments of the plastron tell little. One piece appears to 

 belong to the right hypoplastron and to bear a part of the base of 

 the buttress. Attached is a fragment of the mesoplastron. At the 

 suture between the two bones the thickness is 6.5 mm. Another frag- 

 ment, perhaps the inner end of the mesoplastron, is 8 mm. thick. On 

 a fragment of a costal plate the sulcus bounding laterally a vertebral 

 scute is 16 mm. from the neural border. Taking into consideration 

 the width of the neural bones, the vertebral scutes must have been 

 about 55 mm. wide. 



Figs. 1 and 2 of Plate 11 represent the three plastral bones in- 

 cluded under the catalogue number 6553. The right hypoplastron 

 (Plate 11, iig. 1) has a length of 43 mm. At the hinder inner angle the 

 thickness is I mm.; at the middle of the length, on the suture with its 

 fellow, the thickness is S mm.; at the anterior inner angle, 6 mm. No 

 part of the free border behind the inguinal buttress remains; hence 

 the width of the hinder lobe can not be determined. It could not 

 have been far from 90 mm. The mesoplastron (Plato 11, Iig. 1 ) has 

 a width of 23 nun. near the inner end; but even within a distance of 

 20 mm. the width has increased to 30 mm. At its inner end this 

 bone i- 7.5 mm. thick, but the thickness becomes somewhat reduced 

 outward. The left mesoplastron was evidently wider at the inner 

 end than the right, for it certainly articulated with the right hypo- 

 plastron on an oblique line 10 mm. long and probably with the right 

 hyoplastron also. The left hypoplastron (Plate 11, fig. 2J agrees in 

 all essential respects with the other. There is no possibility that the 

 bone is the hyoplastron. 



On viewing the lower side of these bones one is struck with the 

 irregularity of the median sulcus. Between the abdominal scutes it 

 formed a great loop, toward the right in one individual and toward 



