JOURNAL OF CONCHOLDGY. 365 



THE MARINE MOLLUSCA OF MADEIRA. 



By the Rev. R. BOOG WATSON, B.A., F.R.S.E., F.L.S., F.G.S., 



President of the Conchological Society of Great Britain and Ireland. 



(Read before the Conchological Society, Dec. 20th, 1890). 



Madeira is a group of small volcanic islands which rise steeply 

 out of deep water some two hundred miles south of Gibraltar 

 and about three hundred miles from the west coast of Africa, 

 from which they are cut off by a deep submarine depression. 

 They include— 



1. Madeira proper. — 35 miles long and 14 miles broad, 

 rising to over 7,000 feet above the sea. 



2. Porto Santo. — 30 miles N.E. of Madeira, but with deep 

 water between; 1,600 to 1,700 feet high. 



3. The Desertas. — Three uninhabited islands, which are 

 respectively 300, 1,600 and 1,300 feet high. They lie 

 twelve miles off the eastern extremity of Madeira, but 

 connected by a narrow submarine bank 70 fathoms 

 below water. They stretch 15 miles S.E., are nowhere 

 more than a mile wide, and are cut through by two 

 narrow and shallow sea channels. 



4. The Selvagens, which belong to this group rather politi- 

 cally than geographically— for they are cut off by very 

 deep water, and are distant 150 miles to the S.S.E. of 

 Madeira, while only 100 miles north of Teneriffe. They 

 are three uninhabited islands, separated some ten miles 

 from one another. The largest is three miles long by 

 three-quarters of a mile broad, and 300 or 400 feet high. 



The marine mollusca of this group of islands, so far as I 

 possess them, were, in the main, gathered by myself during a 

 residence which extended from 1864 to 1874. 



