PROTOSTEGID^:. 1 99 



of the bone is traverst by a prominent ridge, the summit of which anteriorly is about 10 mm. 

 wide and which expands posteriorly to the condyle. The sides of the ridge are formed by two 

 bold grooves which run backward and outward from the front of the bone. Whether or not any 

 portion of the basisphenoid is present in the fragment of bone 60 mm. long from the occipital 

 condyle is not certain. Fig. 254 is a section taken near the front of the fragment. The summit 

 of the ridge has been eroded off. 



The carapace is represented by the midline and the ribs of the left side. It resembled that 

 of P. gigas, as represented by Wieland, but the ribs are free from one another to points nearer 

 the midline. The neurals are crusht down against the vertebrae and most of them have been 

 subsequently eroded away. The boundaries ot none can be traced. The distance from the 

 base of the first rib to that of the tenth is close to 800 mm.; the length of the first rib is 205 mm., 

 that of the fifth at least 655 mm. The carapace must have had a length of about 1250 mm. 

 and a width of about 1500 mm. The ribs are free from the adjoining ones to about 120 mm. 

 of the midline. 



Large portions of the plastron are preserved, but all have not yet been made available for 

 study. The right hypoplastron is nearly complete. Its lower surface is traverst by a low 

 longitudinal ridge. The length of the bone along this ridge is 400 mm. The width is nearly as 

 great. The right and left borders are furnisht with numerous digitations. At the hinder end 

 is a notch for the reception of the xiphiplastron. Most of the process of the hypoplastron 

 which joined the xiphiplastron on its outer border is broken away. 



The xiphiplastron (fig. 246, xiph) is remarkably thin, being nowhere more than 10 mm. 

 thick. It is not so abruptly turned toward the midline after being freed from the hypoplastron 

 as is that of P. gigas. Its length was originally close to 375 mm. Beyond the hypoplastron 

 both of the borders are acute; the inner is the thinner. The outer border joined, for more than 

 the proximal half of its length, a process of the hypoplastron. 



The left hyoplastron (fig. 255) is present. Unfortunately many digitations are lost, so 

 that not all its dimensions are determinable. From the hyohypoplastral suture to the 

 anterior end the length is 580 mm., measured on a straight line. From the just-named suture 

 to the bottom of the axillary notch the distance is 300 mm. The entire width of the bridge was 

 not far from 625 mm. The low ridge seen on the hypoplastron is continued forward on the 

 hyoplastron. The suture between the hyoplastron and the hypoplastron was evidently consid- 

 erably shorter than in P. gigas. Here the bone is about 25 mm. thick. 



The T-shaped entoplastron (fig. 246) is preserved, but lacks much of the lateral wings. 

 The lower surface is mostly convex, but on the outer end of each wing it is slightly concave in 

 all directions. The visceral surface is concave from side to side. Near the front border, at 

 a distance of about 25 mm. from the midline, begins a broad groove, quite deep at first, but 

 becoming shallower on the wings. This was almost certainly occupied by the epiplastron. 

 At the midline, near the anterior border, the bone is about 20 mm. thick. About 50 mm. from 

 the midline, on each side, there is a rough surface, as if for a ligament. To this may have been 

 tied the anterior end of the procoracoid process of the scapula. At the outer end of the right 

 wing, as preserved, the thickness of the bone is only 6 mm. Here the surface which was 

 covered by the epiplastron is 65 mm. wide. 



The left scapula, without the procoracoid process, is preserved. Its length, from the upper 

 end to the glenoid fossa, is 275 mm. The coracoid has a length of 425 mm., and a small portion 

 of the distal end is missing. It was not expanded at the distal end. The left humerus is well 

 preserved and not much crusht. The total length is 402 mm.; from the head to the distal end, 

 385 mm. From the head to the lower end of the radial process is 245 mm. The width of the 

 distal end is 185 mm. The ectepicondylar passage is a foramen with a large opening on the 

 articular surface. 



One femur, much distorted by pressure, is present. Its length is 335 mm. The diameter 

 of the shaft is 50 mm. 



Protostega advena sp. nov. 



Figs. 256-259. 



The chelonian remains to which the name Protostega advena is given are the property of 

 Kansas University and have the number 1209. There is no history of the time or place ot 



