202 Proceedings of the Royal Society of Victoria. 



it is also living at the present day, being recorded off Booby 

 Island, in 6 to 8 fathoms. 



Occurrence. — One carapace found ; Jurassic, Greenough River 

 district, West Australia. [2153.] 



Genus Paradoxorhynchn, gen. no v. 



Generic characters/ — Carapace seen from the side sub-quadrate ; 

 dorsal and ventral lines with a slight convexity. Ventral border 

 with a notch at the antero-ventral angle, in front of which is a 

 beak similar to that in Cypridea. Posterior extremity produced 

 into a beak-like process as in Cytherura. Right valve larger, 

 overlapping the left. Habitat, most probably marine. 



Remarks on the genus. — This striking form seems to combine 

 certain characteristics of the genera Cypridea (a freshwater and 

 estuarine genus) with Cytherura and Cytheropteron (marine 

 forms). All the genera named have the two valves unequal, but 

 whereas in Cypridea the left valve is the larger, in Paradoxo- 

 rhyncha it is the right valve which overlaps ; in this respect it 

 agrees with the arrangement found in Cytherura and Cytherop- 

 teron. In the salient, almost wing-like, extension of the postero- 

 ventral angle, Paradoxorhyncha further agrees with Cytherop- 

 teron, and the real relationship of the new genus probably lies 

 nearer the last-named genus. 



Paradoxorhyncha foveolata, gen. et sp. nov. 

 (Plate XXIII., Figs. 1, 1^, 1^). 



Specific characters. — In addition to the above features, presum- 

 ably generic, the following may be added. Carapace thickest at 

 the posterior third. Seen from the side, the interior margin is 

 obliquely rounded at the angles, making the anterior extremity 

 narrow ; flanged on the extreme border. Surface of valve steep 

 towards the ventral border, gently sloping away to the dorsal 

 margin. Ornamented with somewliat closely set areolae or 

 polygonal pittings, four, five or six-sided. Edge view of valve 

 sub-rhomboidal, tumid. End view depressed cordate. 



1 Since these are founded on a single specimen they must be regarded only as provi- 

 eional, pending the discover}' o( further specimens. 



