1G2 MR. GEOFFREY SMITH ON THE 



The antennal scale is bx'oacl, wibli the inner margin widening 

 sudiienl}- after the terminal spine (fig. 20). 



j\[andibles with two prominent teeth and a serrated lower 

 edge (tig. 24). 



First maxilla with endopodite consisting of a basal segment 

 and a minnte terminal segment (tigs. 15, 23). 



Second maxillipede with penultimate segment bearing an upper 

 lobe which does not project forwards nearly so far as the tip of 

 the terminal segment (fig. 22). 



Third maxillipede without a serial row of bristles, but with the 

 face of the tliird and fourth segments provided with a double 

 fringe of slender crowded hairs. The exopodite exceeds the third 

 segment of endopodite in length (fig, 21). 



Great chela with the carpus long and stout, especially in the 

 male ; on the underside a longitudinal ridge is present, often 

 with slight excavations on either side of it. The surface is 

 smooth ; there is no row of tubercles on the outer border, but 

 there is a conspicuous fringe of downy hairs on the inner border. 

 Succeeding legs with terminal and subterminal joints smoother, 

 with very few bristles. 



Opening of vas deferens situated on a long projecting and 

 complicated pnpilla. 



The keel of the rostrum is flat and smooth ; the lateral carina 

 on carapace also continuous and smooth ; there is no median 

 carina. 



The distance between the tip of the ro.strum and the cervical 

 suture is shorter than between the cervical suture and posterior 

 border of carapace. 



The carapace is smooth ; the abdominal segments are smooth 

 and non-setose. 



The sternal keel is fairly prominent and sharp. 

 The interantennal spine is rounded, and does not end in a 

 sbnrp point (fig. 19). 



The membranous portion of telson and uropods is long 

 compared to the upper calcified portion, and the median spine on 

 the endopodites of the uropods is in consequence situated mesially. 

 Remarhs on the above genus. — In creating the above genus for 

 the reception of the single specie'^, P. bicarinatus, I have been 

 influenced by the following facts. Although P. bicarinaUhs does 

 rot diffei' in any very striking characters from the species which 

 I retain in Erichson's genus CJueraps, yet if it were included in 

 tliis genus it would occupy an altogether isolated position, both 

 as reo'ards structure, geographical distribution, and the fact that 

 from it has probably been derived the large and varied genus 

 Enqaus. For convenience' sake, therefore, and for the purpose of 

 bringing out its peculiar importance in the evolutionary history 

 of tlie Australian Crayfishes, I have after much hesitation 

 decided to sepai'ate it otf from the related forms retained in the 

 •^enus Clwraps. Since P. bicarinatns is one of the oldest-known 

 species from Austi'alin, I had oi-iginally intended keeping the 



