314 DR. H. J. HANSEN ON THE [NoV. 29, 



Asellotct am besten getheilt werden konnen." But two years later 

 Sars added very much to our knowledge of numerous genera 

 of Asellota ; furthermore, in 1895 I saw a very large number of 

 undescribed forms — among which several new genera — unknoAvn 

 to me, and received and studied more closely many examples of 

 Stenetrmm. The question as to the classification of the Asellota 

 can therefore now be reconsidered on a broader base. 



Putting Stenetrium aside, it will probably be admitted that the 

 differences in the pleopoda between Asellus (Avith Mancasellus 

 and Coecidothea) a,ncl other Asellota would justify the division of 

 the Asellota into two families. But the structure in Stenetrium 

 gives rise to considerable difficulty. Both in Stenetriimn and 

 Asellus the two anterior pairs of pleopoda in the male and the 

 first pair in the female are quite small, and overlap only a small 

 proximal portion of the following pair, the exopods of which are 

 very large and constitute a complete covering for the respiratory 

 lamellae ; furthermore, in the second pair of the male the end of 

 the endopod is blunt and the exopod not developed as a hook for 

 coupling together the two anterior pairs. 



In all other Asellota the first pair in the female is very large 

 and covers the following pairs completely ; in the male the two 

 anterior pairs constitute together a large operculum formed by 

 coupling of three plates, which cover the following pairs in their 

 whole length and, with a single exception, also in their whole 

 breadth ; the exopods of the third pair are, therefore, generally 

 invisible, in the instance alluded to partly visible from below at 

 the side of the operculum, but in this animal (Plate XXI. fig. 5) 

 they are yet of moderate size, and their inner margin i-ather 

 distant from the mesial line ; furthermore, in the second pair of 

 the male the end of the endopod is acute, the exopod hook-shaped 

 and adapted for coupling. On the other hand, Stenetrium differs 

 from Asellus and agrees rather well with other Asellota in some 

 particulars, viz. : in the male the sympods of the first pair of 

 pleopoda are fused with each other, and the i-ami of the second 

 pair are attached to the inner margin of the sympod ; in the 

 female the pleopoda of the first pair are fused with each othei-, in 

 both sexes the last pair has only one ramus. The genus is dis- 

 tinguished among all other Asellota by the cuiiouiS feature that 

 the endopod of the second pair in the male is without an internal 

 cavity in its distal joint. 



That Stenetrium differs less than Asellus from the other 

 Asellota is thus easily seen, and the question arises as to the 

 systematic importance of the differences and similarities. Ought 

 Stenetriimi to be placed together with Asellus or established in a 

 family of its own ? Considering all particulars, I am now inclined 

 to prefer the lattei- alternative. The Asellota will therefore be 

 divided into three families — Asellidse, Stenetriidte, n. fam., and 

 Parasellidse, n. fam. 



The first-named family comprises the genera Asellus Geoffr., 

 Mancasellus Harg.,and Coecidothea Pack. ; the second family only 

 its single genus ; the Parasellidse all the other genera of Asellota, 



