382 University of Kansas Geological Survey. 



outline for the carapace. The last three ribs are turned 

 backwards with a marked obliquity ; the anterior ones pass 

 directly outwards. The neurals are known only from the pos- 

 terior part, the last four being preserved. The seventh and 

 eighth, the first two preserved, are rather longer than broad 

 and are Y-shaped in section, the two sides meeting in rather a 

 sharp ridge above. The upper part extends posteriorly to 

 articulate with the following bone by an overlapping joint. 

 The ninth is small and closely connected with the tenth, which 

 is the largest of the series. This is rather narrow anteriorly, 

 but expands rapidly posteriorly, to near the end, and then con- 

 tracts abruptly, forming sharp, flat wings upon the sides. The 

 expanded proximal ends of the tenth ribs articulate with the an- 

 terior margin of these wings. Posteriorly the tenth neural ter- 

 minates in a rounded process elevated above the rest of the bone, 

 which extends backward to join a similar process on the anterior 

 face of the pygal. The posterior end of the ninth neural does 

 not overlie the adjoining portion of the tenth, but the two are 

 connected by a separate, thin overlying ossicle of bone which 

 rises above the general level of the carapace and forms an im- 

 bricating joint. The anterior border of this ossicle rises gradu- 

 ally and then terminates abruptly posteriorly, making a very 

 prominent elevation. 



The peripherals are represented by a nearly complete series. 

 The pygal has a greatly thickened anterior border, from which 

 springs a rounded process to join the tenth neural. The pos- 

 terior margin is very thin, giving the bone a triangular form in 

 cross-section. There is a deep notch on the hind margin at the 

 end of a short groove, which begins at about the middle of the 

 upper surface. The peripherals joining the pygal are not so 

 thick in the middle ; the internal border is, however, much 

 thicker than the external. There is no groove or pit for articu- 

 lation with the rib. The next three, probably the ninth, tenth, 

 and eleventh, have much the same characters as that adjacent 

 to the pygal, except that the iuternal border becomes progress- 

 ively thicker. There is a slight sculpture formed by radiating 

 lines from the middle of the upper surface of the bone. - 



