142 



FOSSIL IT RTLES OF NORTH AMERICA. 



Wieland suggested that his type might prove to belong to 0. erosus. However, the latter 

 differs in having thicker bones and a longer nuchal. To illustrate this statement we will 

 consider the seventh peripheral. The length of this is 88 mm., just three-fourths that of the 

 same bone in the type of borealis, yet the thickness of the inner face is 47 mm. 7 mm. more 



This is too great to be due to age or individual variation. The 



ths 



an in the latter species. 





Width. 



length of the nuchal in borealis is 90 

 mm. This bone is not present in the 

 type of erosus, but the left peripheral 

 and first costal show that it extended 

 backward at least 90 mm., and it cer- 

 tainly was still longer. If the animal 

 had grown to be a fifth or a fourth 

 larger the nuchal would have been 

 much more than 90 mm. in length. 

 The anterior peripherals of O. erosus 

 are higher than those of the type of 

 borealis, altho the latter belonged to a considerably larger individual. 



( )n comparing the bones of borealis with those of Cope's supposed sopitus in the 

 American Museum of Natural History no important differences are observed. The nuchals 

 agree. The surface of borealis is marked by pits resembling rain-drop impressions; but the 

 surface of Cope's specimen is so markt to some degree, and a larger specimen referred to the 

 species has such impressions in abundance. Some differences do appear, when careful compari- 

 sons are made among the measurements of the peripherals, but these fall within a few 

 millimeters. Greater differences may be observed between other specimens which are regarded 

 as belonging to 0. borealis. Figures and measurements are presented above of various parts 

 of Wieland's specimen. A portion of these are taken from Dr. Wieland's paper, but most 

 of them have been kindly furnisht me by the author. 



Fig. 163 is redrawn from Wieland's figure in the American Journal of Science and reduced 

 by one-fourth making the figures one-eighth the size of nature. 



Figs. 164-168. Osteopygis borealis. Peripherals of type. 



x*. 



164. First left peripheral, with section (164*2) of the 



proximal end. In the section the upper surface 

 is directed toward the left. 



165. Anterior end of third peripheral. 



166. Anterior end of fifth peripheral. 



167. Anterior end of sixth peripheral. 



168. Anterior end of seventh peripheral. 



Fig. 164 presents the first left peripheral from above, together with a view of the end 

 which joins the nuchal bone; figs. 165, 166, 167, and 168 represent the anterior ends respect- 

 ively of the third, fifth, sixth, and seventh right peripherals. 



I he length of the first neural is 102 mm.; its greatest width is 55 mm. The first costal 

 has a maximum width of about 120 mm. The second is 90 mm. wide at the costo-vertebral 

 sulcus. The first vertebral scute is about 285 mm. wide; the second, about 180 mm. 



The plastron (fig. 163) in general resembles that of 0. gibbi; but the fontanels appear to 

 have been larger and the bridge was wider. The latter has a width of 138 mm. The whole 

 plastron had a width, taken across the hypoplastra, of about 520 mm. The hyoplastron 

 extended forward from the hyohypoplastral suture 138 mm. 



