408 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



extend in a posterior direction. There is no perceptible inequality in 

 length. The unguli are bifid. 



Two specimens were sent by Mr. Heath from Monterey Bay, Cali- 

 fornia. 



Type.Ca,t. No. 22577, U.S.N.M. 



IV. ASELLOIDEA or ASELLOTA/* 



Legs of the first pair not cheliform. Uropoda terminal, biramous. 

 Pleopoda exclusively branchial, the first pair in the female generally 

 transformed into a single operculum covering the succeeding pairs.. 

 Epimera very small or obsolete. All the segments of the abdomen 

 fused together, although occasionally one or two short segments are 

 partially visible anterior to the terminal segment. 



Pleopoda in female reduced in number, only four pairs being present. 



ANALYTICAL KEY TO THE FAMILIES OF ASELLOIDEA. *> 



a. First pair of pleopoda in the male not coupled with the second pair; the peduncles 



short. Second pair small and situated below the first pair. Third pair in both 



sexes forming a compound operculum. First pair in female small. 



b. Peduncles of first pair of pleopoda in the male free. First pair of pleopoda in 



female consist each of a small peduncle and a single branch. Second pair of 



pleopoda in male with branches attached at the distal end of the peduncle, 



the inner branch not geniculate, the distal joint having an inner cavity; outer 



branch nearly as long as inner branch. Fifth pair of pleopoda with both 



branches Family XV. ASELLID^E 



b f . Peduncles of first pair of pleopoda fused in the male. First pair of pleopoda in 

 female with branches fused, forming a small operculum. Second pair of pleo- 

 poda in male with branches attached at the distal end of the inner margin of 

 the peduncle, the inner branch geniculate, the distal joint without a cavity; 

 outer branch much shorter than inner branch. Fifth pair of pleopoda each 

 consisting of only a single branch Family XVI. STENETRIID^; 



See Sars for characters of superfamily, Crust, of Norway, II, 1899, p. 94. 



^ Doctor Hansen (Proc. Zool. Soc. London, 1905, II, Pt. 2) divides the Asellota into 

 but three families the Asellidse, the Stenetriidte (a new family proposed by him), 

 and the Parasellidse which includes all the other Asellota, and represents the fam- 

 ilies Munnidse, Janiridse, Desmosomidae, and Munnopsidae. His basis of classifica- 

 tion is on the structure of the pleopoda alone. Although the structure of the 

 pleopoda in this group forms excellent characters for a basis of classification, other 

 characters must not be wholly disregarded, nor must all other characters be made 

 subservient to this character alone. The Munnidfe, Janiridie, and Munnopsidse form 

 distinct groups which differ in structures quite as essential as those recognized in 

 other families of the order. The differentiation of the legs of the Munnopsidee into 

 an anterior and a posterior series, the division of the thorax into an anterior and a 

 posterior portion, the two being quite dissimilar, are structural differences whicii can 

 not be ignored. The genus Pseudarachna Sars has the posterior legs distinctly nata- 

 tory and fringed with plumose cilia, although the joints are not as much dilated as in 

 the other genera of the family. The Munnidse form also a well differentiated group 

 well separated from the Janiridse, the characters of which are given in the follow- 

 ing key. 



