10 



THE UPPER TRIASSIC OF WESTERN TEXAS. 13 



A NEW GENUS OF THE STEGOCEPHALIA, BUETTNERIA PERFECTA. 



The specimen here described, No. 7475, University of Michigan, was found in the 

 breaks of Sand Creek just south of Cedar Mountain, in Crosby County. It lay in a 

 dark-red, mud-lump conglomerate with some finer material, the deposit of an old river- 

 wash. The undistorted skull is unique in the perfect preservation of the bones and the 

 minutiae with which the osteological details may be traced. The matrix was readily 

 removed from the bones of the lower surface, leaving them clean and white, except 

 where stained red or brown by iron. The rugose upper surface was less readily freed, 

 but the matrix came away very clean, revealing the pits and ridges and all the details 

 of the sutures and the slime-canals. There is no distortion of the bones of the upper 

 and lower surfaces, but the edges of some of the slender bones which form the walls of 

 the brain-case are slightly crumpled and injured by decay. No parts are missing 

 from the upper surface except the major part of the left squamosal, the extremities of 

 the tabulare, and the extreme posterior tip of the right maxillary. On the lower surface 

 a part of the distal end of the left pterygoid is missing, there is no trace of the stapes, 

 and the otic opening is extremely large; for reasons given in the body of the paper it 

 is believed that this region was largely cartilaginous. 



The upper surface of the skull. The form and arrangement of the various elements, 

 the position of the slime-canals, and the character of the sculpture are shown in figure 

 1 A, and plate 1, fig. A, and do not need extended discussion. The general resemblance 

 to the skull of Anaschisma from the Popo Agie beds of Wyoming is apparent, but the 

 arrangement of the teeth and the bones of the lower surface show that the two forms 

 can not be placed in the same genus, and render it doubtful whether they should be 

 placed in the same family. A comparison with Branson's figures 1 shows that the skull 

 was a little broader, proportionately, than in Anaschisma and that the orbits were a 

 little farther forward. Branson was unable to trace all the sutures on the upper surface 

 of his specimen, but, so far as he was able to determine them, the position and relations 

 of the bones correspond as well as could be expected in animals in which there was so 

 much of individual variation. A comparison of his figures with figure 1, A and B, of 

 this paper will show the position of the sutures he was unable to follow, outlining in whole 

 or in part the lachrymals, the quadrate jugals, the jugals, and the maxillaries. In 

 Bucttncria the lachrymals are small elements not reaching to the nares; the maxillaries 

 extend inward anterior to the orbits and form a part of the posterior and lateral bound- 

 aries of the nares; posteriorly they lie upon the sides of the skull, and the postorbital 

 portions are only visible from above as narrow bands. The premaxillaries, nasals, 

 frontals, and parietals exhibit a decided asymmetry. In both the figures and the plates 

 it will be seen that the extremities of the tabulare have been restored; it may easily 

 be that these have been made too large, as the projections are very slight in Anaschisma. 



Not only the sutures but the slime-canals are very perfectly shown in the specimen. 

 (See fig. 1 A. The course of the sutures and the canals shown in the figures was traced 

 with a camera lucida and the lines are almost exactly as they appear in the specimen ; 

 the figures have not been diagrammatized to any extent. The edges of the slime-canals 

 have been traced as straight lines to distinguish them from the sutures.) The course 

 of the slime-canals is similar to that in Anaschisma, but differs in one or two important 

 particulars. Adopting the nomenclature proposed by Moodie, 2 the anterior com- 

 missure and the occipital cross-commissure are absent: the course of the supraorbital 

 canals between the orbits and nares is quite different (compare fig. 14 of Moodie's paper). 



1 Branson, E. B., Journal of Geology, vol. xiu, figs. 1 and 7, 1905. 



2 Moodie, R. L., Journal of Morphology, vol. xix, Xo. 2, p. .513, 1908. 



