A NEW CRUSTACEAN. 573 



ventral teeth. The dorso-veiiti-al thickness of the rostrum is not 

 so great as that of P. varians. 



Eyes. — The eyes are well developed and on fairly long stalks. 

 Antennules. — The antennules are as long as the abdomen with 

 telson. The peduncle when extended does not attain the length 

 of the rostrum by about one-third of the latter, and falls short of 

 the distal margins of the antennal scales by about one-fifth the 

 length of the scales. The shorter ramus of the outer antennule 

 is fused to the longer for about half its length. 



Antennce. — The antennal scales are large, long, and broad, and 

 more than twice the length of the antennal peduncle minus the 

 first segment. They are not quite so wide distally as proximally. 

 The antennal peduncle falls short of the fiist segment of the 

 peduncle of the antennule. 



Mandible. — The mandibles are without palps. Incisor and 

 molar processes are well developed and tipped as indicated in the 

 figure. 



MaxiUuke and Maxillce. — These appendages are a,s figured. 

 They possess no features of systematic importance marking them 

 ofi'from the similar appendages of P. varians. 



Maxillipedes. — These are similar in structure to those of P. 

 varians. The third maxillipedes when extended reach approxi- 

 mately to the end of the antennary peduncle. 



Perceopods. — The second peraeopods are the longest, and when 

 extended they overlap the antennary scale by palms and fingers. 

 The third perseopods are about as long as the first, the fourth a 

 little longer, and the fifth pair are the longest of the posterior 

 three. The first pair of perseopods attain almost the apex of the 

 antennary scales when extended forwards. The chelae of the 

 second pair are shorter than the carpus, and the dactylus slightly 

 more than two-fifths length of palm. 



Telson. — The telson is longei- than the preceding segment. It 

 terminates in the mid-line with a spine. The armament consists 

 of two pairs of stout spines and one pair of setae. The latter are 

 situated one on either side of the median spine. The posterior 

 margin of the telson differs distinctly in shape from that of 

 P. varians. Two pairs of spines are present on the dorsal surface 

 of the telson. 



Conclusion. 



Palcemonetes australls occurs in the fresh-water of rivers some 

 distance from the coast in West Australia, and is also found in 

 shallow lakes on the coastal plain. 



Females bearing eggs which have been just extruded have 

 been captured in September (Bibra Lake), and others bearing 

 embryos not far from the hatching stage have been collected 

 on January 1st from Gin Gin Brook. This would indicate that 

 the breeding season coincides with the early months of the 

 summer — the dry season. Most of our West Australian fresh- 

 water animals breed in the winter or spring, and many possess 



Proc. Zool. Soc— 1915, No. XL. 40 



