Section 2. 



Monstrilloida genuina. 



Remarks. In this section are comprised the typical Monstrilloida, the 

 general characters of which coincide with those given below for the sole 

 family as yet representing the section. 



Fam. Monstrillidae. 



General Characters. Body more or less slender and elongated, with the 

 anterior division only slightly dilated and not sharply marked of from the 

 posterior. Head and 1st trunkal segment completely coalesced, forming together 

 a very large segment of a more or less cylindrical shape, and as a rule occupying 

 rather more than half the body, its anterior extremity obtusely truncated, without 

 any rostral prominence; ventral face of the segment in the greater extent of 

 its length quite smooth, exhibiting no traces of either posterior antennae or 

 any oral appendages, being only provided in the median line with a small 

 tubular process, from which a short canal leads to the inner substance of the 

 body; the latter in female specimens retracted from the walls of the segment 

 in a most peculiar manner, so as to form a rather narrow band-like chord 

 passing through the axis of the segment. Exposed part of trunk composed 

 of 4 well defined segments gradually diminishing in size behind. Tail poorly 

 developed, with the number of segments more or less reduced, and exhibiting 

 well marked sexual differences. Caudal rami, as a rule, short, but provided 

 with strong plumose setae, the number of which is somewhat variable in the 



