BY C. W. DE VIS, M.A. 127 



narrower than in the previous example. On the inner surface 

 the skeletal rib is somewhat narrower ; it is preserved in place 

 to the end of its surface of attachment which is much further, 

 25 mm,, from the free edge. 



Each of the plates described is about 6 mm. in thickness. 

 The nearest approach to the pattern of their sculpture is made 

 by an American Eocene species figured by the U.S. Geological 

 Survey; vol. IV, Palfeontology. p. 51, pi. 25, p. 10a. 



The distal moiety of a right pleural plate 38-5 mm. broad 

 at its free border and 34-5 mm. at a distance of 45 mm. from 

 the border is shewn on PI. X., fig. D. Near the border and 

 parallel with it three undulating ridges pass from side to side ; 

 on the rest of the upper surface similar but stroncrer ridges, 

 preserving a generally transverse direction, become tortuous, 

 interosculate, or, joined by fainter descending spm's, form with 

 them an irregular network ; the free border is narrow and 

 slightly shelving. On the inner surface the rib occupies the 

 posterior half of the plate ; it is 22 mm. broad and is attached 

 to the whjle length of the surface above it ; the inner face of the 

 free edge of the plate is bevelled oft" narrowly anteriorly but more 

 broadly as it passes over the extended rib ; the bevelled surface 

 is impressed by a shallow groove. 



Part of the proximal end of a similar pleural p'.ate, PI. 20, 

 fig. E, differs from the preceding chiefly in having its rib a little 

 removed from its anterior edge. In the subject of fig. B we 

 have the distal end of a pleural plate from a young carapace ; 

 this also has the characteristic pattern of pleural sculpture, 

 with a broad margin and a rib occupying the middle two-thirds 

 of the inner surface. Fig. C represents a fragment of a pleural 

 from near the free border. 



The neural plate shown in fig. A, 1-2, is in form an un- 

 symmetrical hexagon with anterior lateral sides shorter than 

 the posterior laterals and the posterior side concave. The outer 

 surface is covered with a network of low ridges ; the inner has 

 the usual double ridge for tlie attachment of a vertebra. A left 

 half of a second example of this plate is not figured. 



Luc: Durling Downs. One of the specimens was obtained 

 by ^Y. Hann's Northern lixpedition in a locality unrecorded. 

 [Til he ( 'ii)iti)n(t'tl,] 



