122 



This delicate species grows to the height of one third of an 

 inch, and is of a light straw colour ; the cells are on both 

 sides, running from the base to the apex, are quadrangular in 

 form, but enlarged about the centres. It is dichotomously 

 branched, and the terminations of the branches are axe- 

 shaped, or truncated. 



Fleming seems to be in doubt, whether to consider this 

 as a distinct species, or a variety of the preceding; he 

 founds his doubts on a specimen sent him by Montagu; but 

 the specimens I have seen do not countenance such a doubt. 

 It much more resembles the Flustra truncata ; from which 

 there appears to be no sure mark of distiction, 



* * Foliaceous, with cells on one side only. 



FAN SHAPED SEA-MAT. F. Avicularis. Cells quad- 

 rangular, in three or four rows, with a spine at each distal 

 angle on the external edge, and one on each side below, 

 pointing across the cells. 



Ellis' Coral., pi. 38, fig. 7. Flustra avicularis, Fleming's 

 Brit. An., p. 536, no. 144. Crisia flustroides, Lamouroux's 

 Cor. Flex., p. 141. Johnston's Brit. Zooph., p. 286, pi. 36, 

 figs. 3, 4. 



Hab t On stones, shells, especially the Pinna ingens and 

 Pecten maximus, on the back of the larger spider crabs, 

 from deep water; common. 



This very beautiful and delicate species varies in height to 

 one inch, it is however sometimes so small as not to exceed 

 one fifth of an inch ; when living it is of a very delicate 

 flesh colour, but in dying it changes to a dull brown. 



The polypidom is compressed, thin and divided dicho- 

 tomously into flat segments which terminate in a truncated 

 manner; when living it is very elastic, but when dead it is 

 so friable that it falls to pieces on the slightest handling. 

 The cells are on one surface only of the polypidom, the 

 other being plain or marked only by the attachments of the 

 bases of the cells. They are quadrangular in form, and are 

 arranged into from three to five alternate rows. The su- 

 perior and external margins have a single stout spine, one on 

 each angle, between which rises a pearly globular operculum. 

 Inferiorly to these are two other spines, which pass trans- 

 versely across the diameter of the cell, reaching nearly 

 about the middle. On the external margins of the cells 

 there is frequently to be observed, a very curious and re- 

 markable appendage in the shape of a bird's head. When 

 the specimen is living this organ is continually employed in 

 opening and closing its bill; but of what service it is to the 



