408 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



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

 length. The unouli are bifid. 



Two specimens were sent ])y Mr. Heath from Monterey Bay, Cali- 

 fornia. 



Ti/pe.— Cat No. 22577, U.S.N.M. 



IV. ASELLOIDEA or ASELLOTA." 



Leg's of the first pair not cheliform. Uropoda terminal, l)iramoiis. 

 Pleopoda exclusivel}' l)ranchial, 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 occasionalh' 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 ijleopoda 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 tirst pair of pleopoda in the male free. First pair of pleojioda 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 



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 jjair 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 liranch. Fifth pair of pleopoda each 

 consisting of only a single branch Family XVI. Stenetriid^e 



a 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 Asellidjie, the Stenetriid;ie (a new family proposed by him), 

 and the Parasellidse — which includes all the other Asellota, and rei)resents the fam- 

 ilies Munnidie, Janirid;e, Desmosomida% and Munnopsid;e. 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 i-lassiiication, other 

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

 subservient to this character alone. The Munnidfe, Janiridfe, and Munnopsidaj 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 Munnopsida^ 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 which can 

 not be ignored. The genus IWrnhiraclnni 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 ]\Iunnid;e form also a well differentiated group 

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

 ing key. 



