NO. 1350. NATURAL ITISTORY OF THE TSOPODA— RICHARDSON. 11 



being- chelate, the second pair, with the exception of Pagurapseudes 

 Whitolegge, terminating in a l)roa(l flat joint surrounded with numer- 

 ous llattened spines. The Arcturidie have the four anterior pairs of 

 legs differentiated from the other three pairs; they are slender, feeble, 

 directed forward, and strongly ciliated on their inner margins with 

 long slender hairs; the last three pairs are entirel}' different in struc- 

 ture, being ambulatory in character. 



The Munnopsida^ have the first pair of legs shorter than the three 

 following pairs and prehensile in structure; the three following pairs 

 are ambulatory and greatly elongated; finally, the last three pairs are 

 fitted for swinnning, l)eing natatory in character, and have the two 

 distal joints flattened and provided with numerous hairs and spines. 

 Among the Janiridse there is more or less modification in the structure 

 of the first pair of legs in several genera. Stenetrlum Haswell and 

 Jamna Bovallius have the first pair of legs chelate, these being the only 

 genera of this group which are so characterized. The genus Carpias 

 Richardson, belonging to the same family, is remarkable for the 

 greatl}^ elongated first pair of legs and the peculiar development and 

 enlargement of the joints. In many genera and some families of 

 Isopods the first pair, the first two pairs, the first three pairs, or all 

 the legs are prehensile, the propodus being enlarged or dilated and the 

 dactylus retiexed. 



The Serolid.e have the last pair of legs small and feeble in proportion 

 to the others, correlated with the rudimentary condition of the sev- 

 enth thoracic segment. In Tanais stanfordi Richardson the second 

 pair of legs are small and feeble, although similar in structure to those 

 following. 



Mfunna neozelandica Chilton from New Zealand is a species in which 

 the first gnathopods of the adult male have a remarkable form, with 

 the second joint small, the third "-very thick and strong, hollowed 

 anteriorly to receive the distal end of the limb when bent back; carpus 

 expanded distall}", mallet shaped; propodus small and rounded.'' 



In certain genera of the Apseudidie, Ajxseudes Leach, Pi( rajpseudes 

 Sars, and Sphyrajms Norman and Stebbing, there is a minute and 

 inconspicuous two-jointed exopod at the base of the first and s(H'ond 

 gnathopods. The exopod is absent on the first pair of legs in l\igura- 

 pseiides Whitelegge. The genus Leiopus Beddard, belonging- to this 

 family, has a three-jointed exopod at the base of both pairs of gnatho- 

 pods. The supposed function of these exopods is to keep a constant 

 current of water in the branchial chamber, and thej' are in rapid 

 niov(Mnent in the living animal (St(d)bing). 



Papillose adhesive processes, which are supposed to represent exo- 

 pods, are developed on the coxal joint of all the legs of Kepon Duver- 

 noj- and Leidya Cornal ia and Panceri. although they are in a rudimentary 



