150 MEMBRANIPOIIID/E. 



underside of stones, between tide-marks, frequent; more 

 rarely in shallow water " (Alder) : Shetland, on stones, 

 between tide-marks (A. M. N.) : Birtcrbuy Bay (G. S. B.) : 

 Isle of Man. between tide-marks ; Salcombe, Devon ; 

 Cornwall (T. II.) : St. Andrews, abundant between tide- 

 marks (Dr. M'lutosh). 



GEOGRAPHICAL DISTRIBUTION. France, south-west 

 (Fischer). 



From M. lineata the present species is readily distin- 

 guished by its elongate closely-set cells, its numerous stout 

 spines, and its remarkable avicularium. In the latter we 

 have a very interesting transition-form, standing between 

 the highly specialized movable appendage which we meet 

 with in the genus Bugula, and the ordinary avicularium 

 of the Membraniporidte. A short and very slender pedicle 

 supports the avicularian cell, which widens gradually 

 upwards above it, so that the whole structure presents a 

 somewhat clavatc figure. Above, it is obliquely truncate, 

 and terminates in a pointed beak-like apex. On this 

 truncate portion the acute mandible is placed, directed 

 upwards towards the beak. The whole appendage bears a 

 very close general resemblance to a cell of the common 

 Eucratea chelata. 



The pedicle near its point of junction with the base of 

 the cell is extremely slender, and composcd : of very delicate 

 material ; and it is quite possible that the appendage may 

 possess a certain amount of mobility, even though not 

 endowed with any special motor apparatus. On this 

 point, however, I cannot speak with certainty, as I have 

 never had the opportunity of examining the species in a 

 living state. Alder describes the avicularia as "developed 

 sparingly on any part of the margin of the cell;" but, 

 according to my observations, they arc very constant in 



