12G THE LESSEE CHELONIAN3, ETC. 



have not yet received." | So far as the writer is aware, this is 

 the only intimation we have had of the former existence of a 

 Trionyx in Austraha. The remains which he has to adduce in 

 confirmation of Mr. Clarke's discovery consist of a neural plate, 

 the left moiety of a similar plate, portions of four pleural plates 

 from the mid-region of the test, and two posterior pleurals. 



It will be convenient to commence with these last, since 

 they offer the most salient features for recognition. The left 

 plate (PI. X., fig. F) is perfect, with the exception of a small 

 piece lost from the upper angle. This plate is triangular in 

 form ; its line of suture with its fellow of the opposite side is 

 nearly straight, and 38-5 mm. in length ; that separating it from 

 the pleural antei'ior to it is somewhat convex and 50 mm. in 

 length ; its free distal edge is undulatory and 47"7 mm. long. 

 Its outer surface is traversed by Fix raotleratcly strong nodular 

 longitudinal ribs which extend nearly or quite to a marginal 

 band without sculpture. In the distal half of their course the 

 descending ribs are crossed by much narrower and more closely 

 set undulating ridges which, towards the proximal angle of the 

 plate, gradually become obsolete. The free margin is on the 

 average O'omm. broad ; it is a little roughened by minute eleva- 

 tions of the surface which is convex and bevelled off to an obtuse 

 edge. Attached to the inner surface of the plate and 5 mm. 

 from the anterior edge is a portion of a rib 9 mm. broad and 

 21 "5 mm. long, running parallel with the edge; the surface of 

 attachment extended distad 6 mm. beyond the present broken 

 end of the rib, as is shewn by the scar left on the surface of the 

 plate, but for the remaining space of mm. the rib was free 

 from the plate above it. 



An ultimate pleural from the opposite side of a different 

 individual (PI. X., fig. G) is of rather larger size, as its free border 

 measures 53 mm. in length, but is more imperfect, its proximal 

 angle being entirely lost. The ribs in this example are the 

 same in number but much stronger in development : the trans- 

 verse ridges, on the other hand, are but little larger ; an addi- 

 tional rib descends for a short distance between the middle pair 

 and a less distinct intercalated rib is recognizable between the 

 second and third anterior ribs ; the free border is considerably 



* Ik'v. W. B. Clarke, " Geological Magazine," Vol. YI. 186'.», p. 384. 



