MEMBRA.NIP011A IMBELLIS. 161 



west coast ; Brixhara^ from the trawl-boats ; off the 

 Deadman, 60 fathoms (T. H.) : The Minch ; Shetland, 

 rare, 40-50 fathoms, 5-7 miles east of Balta (A. M. N.). 



This species, which seems to be essentially a deep-water 

 form, is distinguished from M. Flemingii by the much 

 larger size of its cells, and the total absence of a cal- 

 careous lamina and of all spines and avicularian appen- 

 dages. Mr. Busk regards it as '^ an unarmed variety ^^ of 

 the last named ; but it is not the mere absence of the cha- 

 racteristic armature of M. Flemingii that differentiates 

 the present form. The calcareous lamina, covering in the 

 lower portion of the area, which is so important a character 

 of the normal M. Flemingii, is universally wanting in 

 M. imbellis. In the latter the area is wholly roofed in 

 by a membranous covering as in M. lineata and M. La- 

 croixii. At the same time it should be remarked that 

 the spines and avicularia (which constitute its armature) 

 are most characteristic features of M. Flemingii. The 

 former may be wanting at times in old and worn spe- 

 cimens ; but there is generally a hole or stump to show 

 where they have been. The avicularia, I believe, are 

 always developed in greater or less number on the 

 form with calcareous lamina, to which I restrict the 

 name Flemingii ; but in M. imbellis not a trace of 

 such appendages is to be met with in any stage of 

 growth. Mr. Busk, I venture to think, has credited the 

 former species with a larger amount of variability than 

 really belongs to it. Certain it is that, of the figures 

 which he refers to it in his admirable ' Catalogue,' one or 

 two at least of those which diverge most widely from the 

 normal type {e.g. plate civ. figs. 2 and 4, and probably 3) 

 are representations of totally distinct species. 



Apart from the important differences to which I have 



M 



