246 Transactions. — Zoology: 



narrows somewhat abruptly, so that a portion of the margin 

 here is very convex ; I have never, however, seen it produced 

 into a distinct point, as shown in Dana's figure of P. tenui- 

 cornis, and think this must be due to an exaggeration on the 

 part of the artist. (Compare figs. 3 and 4 of Plate X.) The 

 spines on the under surface of the joints of the peduncle of the 

 antenna are often entirely absent in small specimens, even 

 though sexually mature. The length of the antenna varies 

 considerably (see table below) : it may sometimes, as in Nel- 

 son specimens, be greater than that of the body itself. The 

 great claws, again, vary very greatly, both in proportion to the 

 body and in the shape and relative size of the different joints. 

 Large, well-developed forms have the propodos long and 

 thick (i.e., not compressed), and are easily distinguished from 

 those of P. neo-zelanicus ; but in others the propodos is 

 somewhat compressed, and is not so long in proportion to its 

 breadth, thus approximating in appearance to those of P. 

 neo-zelanicus. In the large specimens the propodos is often 

 fully three times as long as broad, but in some specimens from 

 the Thames, Greymouth, &c., it is not more than twice as 

 long as broad, and in these it does not widen distally as it 

 usually does in the others. In the same way the spines on 

 the great claws vary to quite as great an extent as those on 

 the carapace, but it would be tedious to enter into detail. In 

 the Lake Koto-iti specimens those on the propodos are nearly 

 all more or less tubercular, instead of being distinctly spinous, 

 as is usually the case. The propodos, especially in the 

 smaller specimens, often bears a few scattered hairs, but these 

 are never arranged in tufts as in P. neo-zelanicus. 



The distinctness of the infero-posterior angle of the abdo- 

 minal pleura also varies very considerably, and it is sometimes 

 quite rounded, as in P. neo-zelanicus. 



Desceiption of Avon specimen of P. nco-zelamcus. 



As this specimen agrees in many respects with the one of 

 P. i)lanifrons already described, I shall only give those points 

 in which it differs. The length of the body is 4-85in., greatest 

 breadth l-2in., length of antennte 3-5in., of great claws 3'5in. 

 The branchiostegites bulge considerably in the centre, so that 

 the breadth here is much greater than in front of the cervical 



groove. The rostrum has — ^^ ^^ ^^® formula for its spines, 

 and is only slightly depressed. The median ridge behind the 

 rostrum begins on a level with the anterior of the two spines 

 at the side, and extends about three-fourths of the way back to 

 the cervical groove. The spines on the carapace are very 

 numerous, several of the groups running into one another. 

 They may be briefly described as follows, using the same 



