SCHIZOPOUELLA AURICULATA. 263 



undoubted 5. aurlculata I have met with large avicularia 

 exhibiting the same type of form as those just described. 

 The short oval avicularia correspond with an early 

 developmental stage in the normal form. The total 

 absence of the umbo and the immersed condition of the 

 avicularium seem to be the only really distinctive points ; 

 and these are of comparatively small importance. 



These varietal modifications of the avicularium, of 

 which we have many instances, have a high morphological 

 interest. They illustrate the instability of this element of 

 the structure, to which I have elsewhere referred, and 

 should teach us caution in employing it as a diagnostic 

 character. 



HABITAT. On shells, stone, Coralline, and occasionally 

 weed (Ptilota plumosa, Finmark), from very shallow to 

 deep water. 



LOCALITIES. Widely distributed, and common. The 

 Minch ; Shetland, to 100 fathoms (A. M. N.) : Orkney 

 (Lieut. Thomas) : Northumberland, rare (Alder) : Norfolk 

 (Hassall) : Suffolk ; Isle of Wight (Busk) : Isle of Man ; 

 Devon; Cornwall, 60 fathoms (T. H.) : Scilly (M' An- 

 drew) : Belfast (W. T.) : Dublin (Hassall) : &c. Var. a. 

 coast of Cornwall, 30 fathoms; var. (3. Guernsey (T. H.). 



GEOGRAPHICAL DISTRIBUTION. Greenland (Torell) : 

 Finmark (Loven) : Spitzbergen, on Nullipores and stones, 

 3-30 fathoms (Smitt) : Bergen (A. M.N;) : Gulf of St. 

 Lawrence (Dawson) : Algiers (J. Y. J.) : JEgean Sea, 

 var. (E. Forbes) : ?E. Falkland Islands, 4-70 fathoms 

 (Darwin) : Glenelg (T. H.). Var. /3. ? Red Sea or Medi- 

 terranean. 



RANGE i\ TIME. Normal and var. a., Sicilian Pliocene, 

 Bruccoli (A. W. Waters). 



