THE LAND CRAYFISHES OF AUSTRALIA. 119 



median teeth and one smaller tooth in front, and a row of smaller 

 serrations behind. 



The first maxilla? (PI. XVI. figs. 18 & 19) have the endopodite 

 without any trace of a flagellum. 



The second maxillipede has the penultimate segment broad, 

 projecting nearly as far as the terminal segment (fig. 21). 



There is an entire absence of filaments from the epipodite of 

 the first maxillipede. 



The third maxillipede may have the exopodite normal, reduced, 

 or absent. There is a great development of filtering apparatus 

 of bristles and hairs on this and on all the mouth-parts. 



The great chelae show an immense range of variation, being 

 symmetrical or asymmetrical, serrated or smooth, haiiy or 

 comparatively hairless. 



The vas deferens is situated on a simple short papilla. 



The rostrum is reduced, and its lateral keels are either smooth 

 or feebly tuberculated, There are no keels on the carapace, nor 

 are there any spines on the carapace or abdomen, The abdomen 

 is reduced, sometimes markedly so, and it may be hairy. 



The eyes are reduced in size. 



The carapace is very deep (PI. XIV. fig. 12) measured in a 

 dorso-ventral direction, and the distance from the tip of the 

 rostrum to the cervical groove is always longer than that from 

 the cervical groove to the posterior border of the carapace. 



Key to the Sjyecies of the Genus Engajus, 



(1) Last pleiirobraiich present, two flagella oji 1st antenna. 



(A) Exopodite of 3rd maxillipede absent or rudimentary, 



Antennal scale rounded at end without spine E.fossor, 



Antennal scale pointed, last pleurobranch large E. affiii.is. 



Antennal scale pointed, last pleurol)ranch reduced ....,,.., E. vie to Hens it. 



Uropods produced into pointul apices .., -E. phtillocercus. 



Rostrum straight and large with prominent keels E.fultoni, 



(B) Exopodite of 3rd maxillipede well developed E. ctmiciilariiis. 



(2) Last pleurobranch and exopodite of 3rd maxillipede absent 



and only one ftagellum on first antenna., E, hemioirratnhis, 



Eng^us fossor Erichson^ (Pis, XIV.-XVII, figs, 11-22.) 



Astacus {Engmts) fossor Erichson, Arch. f. Naturg, vol, xii. 

 p. 102 (1846). 



Astacus fossor Von Martens, Monatsber, Akad, Wiss. Berlin, 

 1868, p. 618. 



Engceus fossor Haswell, Cat, Australian Museum, Stalk- and 

 Sessile-eyed Crustacea, p, 178 (1882), 



The posterior pleurobranch is present, and is larger than the 

 others. The anterior pleurobranch is very small, 



The posterior arthrobranchs are all very small, consisting of a 

 stalk bearing not more than four or five filaments. 



The exopodite of the third maxillipede is reduced to a very 

 small tubercle (PI. XVII. fig. 22). 



