264 Rev. T. Hincks on the 



systematic value of such peculiarities of growth in a natural 

 system. 



Hab. On Nullipores. 



Range. Cape Verd Islands : var. robusta, Hincks, Algiers. 



Family Cellariidae. 

 Cellaria, Lamouroux. 

 Cellaria Johnsonij Busk. 



This seems to be a common species in the Mediterranean. 

 Range. Madeira ; Algiers ; Bay of Naples ; Shetland. 



Family Membraniporidse. 



Subsection a. Zoarium flexible and foliaceous. 



Flustea, Linnaeus. 



Flustra securifronSj Pallas. 



This species is included in Heller's list, but he has not noted 

 certain peculiarities which belong to the southern form of it. 

 There are commonly two rather strong spines on tiie cell 

 placed one on each side at the top, and the avicularia, in a 

 large proportion of cases, are set obliquely *. 



The front of the ooecia is closed in by a membranous cur- 

 tain, and in those from which the embryo has escaped there is 

 usually at the top of it in the centre an opening somewhat in 

 the shape of a reversed triangle. The definiteness and uni- 

 formity in the position and form of this orifice seem to show 

 that it is due to some special structural arrangement. It has 

 all the appearance of having been caused by the action of a 

 muscle attached to a point in the middle of the upper margin 

 of the membrane, which, in contracting, has drawn a portion 

 of it downward, and so provided for the egress of the embryo. 

 A similar contrivance has been demonstrated in the ovicell 

 of Bicellaria ciliata. 



In Flustra papyi-acea an analogous opening exists. 



Range. Britain (chiefly north) ; Norway ; Spitzbergen ; 

 South Labrador ; Naples. 



* These variations have been mentioned by Waters in his ' Brjozoa of 

 the Bay of Naples. 



