202 THE VOYAGE OF H.M.S. CHALLENGER. 



obsolete organs, there is no anatomical reason why they may not be present in the 

 males as well as the rudimentary mammae in the males of the Mammalia. 



The second pair of pereiopoda is shorter and much more slender than the first, it is 

 chelate, the propodos not being larger than the carpos ; the fingers are slender and 

 correspondingly curved and adorned with a series of distantly planted fasciculi of hairs, 

 and the meros is armed with a few teeth on the outer margin, and two or three on the 

 inner near the carpal articulation. 



The third pair of pereiopoda resembles the second but is more slender and less 

 strongly armed. 



The posterior two pairs of pereiopoda are a little shorter than the preceding, they are 

 more conspicuously armed on the outer side of the meros and carpos and on the upper side 

 of the propodos, which is more slender, than in the preceding two pairs, and the inner 

 distal angle is produced to a short pollex that is about one-third the length of the dactylos 

 and therefore is only sub- or imperfectly chelate. The last four pairs of pereiopoda, like 

 the first, articulate with a process on each side of the median ventral carina, and these 

 processes increase in size and importance, and separate slightly, as they proceed posteriorly. 



The first pair of pleopoda is wanting ; the second and succeeding resemble each other ; 

 they consist of a basisal joint and two compressed branches, having parallel margins 

 thickly fringad with hairs. 



The posterior pair, which helps to form the rhipidura, is broad and corresponds in 

 length with the telson. The inner branch is armed with three or four teeth longi- 

 tudinally placed in the median line and corresponding with a slight elevation ; the 

 outer plate is ribbed in the median line and armed with a few teeth near the outer 

 margin. A diaeresis divides the plate one-third from the distal margin, and is fringed 

 with a regular series of small sharp-pointed teeth, of which the largest exists on the 

 outer margin, and one corresponds with the extremity of the median rib, whence they 

 gradually diminish and disappear on the inner side. The distal portion of all the 

 plates of the rhipidura is submembranous, finely corrugated, and fringed with hairs. 



Astacopsis paramattensis, n. sp. (PI. XXVII. fig. 1). 



Carapace dorsally broad and smooth. Anterior division laterally dentate, posterior 

 division laterally tuberculate. 



Pleon dorsally smooth, laterally tuberculate. Telson denticulate, and posteriorly 

 minutely corrugated. 



First pair of pereiopoda subequal ; surface smooth, margin denticulate ; carpos with two 

 teeth on the inner margin; meros longitudinally denticulate on the upper and lower margin. 



Length (female), 94 mm. (375 in.). 



Habitat. — One specimen taken in the Paramatta River, Sydney, Australia. 



