I 



378 Emerson and Loomis — Stegomus Longipes. 



showing that the dermal bones were paired along the middle 

 line. The premaxillse are short, the nasals are rather long, but 

 the boundaries of the other bones cannot be made out. A 

 vertical break shows the side of the skull imperfectly, as 

 restored in fig. 3, PL XXII. The parts actually present are 

 indicated by the complete line, while restoration is indicated 

 by a broken line. It is a low skull, being about one-third as 

 deep as long. The quadratum is well back, making a long 

 jugal arch. An antorbital vacuity is present though its boun- 

 daries are very imperfectly indicated. The orbit is moderately 

 large, being distinctly bounded off from the temporal vacuities 

 as indicated. It has above it at least two supraorbital bones. 

 That there is a large lateral temporal vacuity is certain. A 

 forward projection of bone in the squamosal region seems to 

 indicate a dividing arcade between this and a supra-temporal 

 vacuity, but the arcade is not complete and is not therefore 

 certain. On the maxilla of the left side one tooth and a part 

 of a second is preserved, showing them to be tiny conical affairs. 

 The depth of the lower jaw is about 3 mm , being a light slender 

 mandible. 



Carapace. — The dorsal side of the body was protected b}^ a 

 double row of plates, on either side. Those along the middle 

 line are wide, their outer edges being flanked with small quad- 

 rate scutes. From the head to the pelvis there are 28 sets of 

 plates, which are narrow and inflexed in the neck region, 

 widen till the middle of the body is reached, and then grad- 

 ually taper toward the tail. The arrangement and relations of 

 these scutes are seen in fig. 2. Each plate of the median row 

 is usually about 4—4 1 '2 mm from front to back. The third and 

 fourth, however, are about half as wide as the rest, while the 

 fifth is much the widest, being wider than the two preceding 

 taken together. Possibly some of this variation is due to the 

 curvature of the neck, but most of it is clearly the bone itself. 

 The rear margin of each scute overlapped the front of the suc- 

 ceeding one, as is clear in the cast of the upper surface. Marsh 

 considered that in his specimen this was not the case, but the 

 fossil shows only the under surface of the scutes and they 

 appear exactly as do those in the specimen under description. 

 Marsh used this character to distinguish Stegomus from Aeto- 

 saurus, but the contrasts must be found in other characters, as 

 is shown later. Along the outer margins of plates 5-9 small 

 quadrate scutes were brought into sight by preparation. The 

 nature of the fossil does not permit further preparation, but 

 doubtless similar scutes occur all along the side of the body. 

 On the cast of the upper surface of the scutes, there are indica- 

 tions that the surface was pitted but the coarseness of the 

 sandstone prevents certainty. 



Vertebral. — Three presacrals are exposed, each deeply bicon- 



