280 Annals of the Carnegie Museum. 



shields. The parietal sends out wings postero-laterally. These wings 

 are sharp and thin anteriorly, but have ridges on their postero-inferior 

 surfaces. Their upper surfaces are slightly convex, but are nearly in a 

 horizontal plane. They do not face upward and forward as in Iguana. 

 The parietal overlaps the squamosal with which it has a long surface 

 of contact. The squamosal is long and sickle-shaped. The shields 

 prevent one from determining how far the bone extends anteriorly. 

 There are no separate mastoid or prosquamosal bones. The quadrate 

 is in place, but not all of it can be seen. It has a posterior longi- 

 tudinal angle or ridge and the posterior upper portion of the bone pro- 

 jects backward. The frontals between the orbits are only moderately 

 thick. 



The mandible is quite thick transversely and is rounded on the in- 

 ferior surface. The post-dentary portion is nearly or quite as long as 

 the dentary portion. It arches outward, the articulate portion being 

 bent inward. The coronoid process is quite high. The teeth form 

 an even row and are only a short distance apart. In the upper jaw the 

 teeth which are visible increase slightly in height anteriorly. Appa- 

 rently their antero-posterior diameters are slightly greater than their 

 transverse diameters. They are low and their apices rounded. 



The hard, osseous shields nearly cover the bones of the skull and the 

 spaces between them. They vary in size, but none are as large pro- 

 portionally as those of Helodermoides tuberculatus Douglass. Their 

 upper surfaces are convex, and the forms of their peripheral boundaries 

 vary with the amount of crowding of the contiguous shields. Some 

 are nearly circular, some four-, some five-, and some six-sided. They 

 are arranged with a fair degree of regularity around the orbits. 

 Each orbit had about twenty of these shields surrounding it in the 

 fringing row or circle ; the next row had at least twenty-three and 

 probably twenty-six. The third row was not continuous, but was in- 

 terrupted beneath the orbit, and the two rows on the opposite sides 

 unite on the median line of the skull between the orbits, thus making 

 five complete rows here. Posterior to the lower portion of the orbit 

 the shields are larger. A central shield is surrounded by five large shields 

 and one small shield. The three concentric rows around the orbits 

 do not include an area on the median posterior parietal portion of the 

 skull, which is covered with about a dozen or more shields which are 

 arranged in the form of a triangle, these short rows composing it ex- 

 tending in the same direction as the contiguous concentric rows. A 



