268 KEY. R. B. WATSON ON THE 



but very distinct white riblet which on the inner face of the shell 

 follows this external line. A similar feature seems to exist in the 

 T. cJilorotica, Gould, a Pacific Ocean species which unfortunately 

 I know only from description, and that (both of Gould * and 

 Tryon t) is too vague and too divergent from the Madeiran 

 shells to allow of guesses as to its relation to the species from 

 Madeira, of which, moreover, the pallets are wanting. 



INDEX-LIST 



of the Sea-dwelling Mollusc a of Madeira. 



I have called this an Index-List in justification of the alpha- 

 betical arrangement adopted. 



Geographical details will be found in the Presidential Address 

 to the Conchological Society for 1890, published in the ' Concho- 

 logical Journal,' vol. vi. no. 11, July 1891; and it will suffice to 

 note here that a special interest attaches to Madeira from its 

 position as a point where the Mollusca of Western Europe, of 

 the Mediterranean, of "West Africa, and even of the North 

 Atlantic and Eastern North America, find a centre of con- 

 vergence. The list of collecting stations is given below. 



To the specific names which follow are added for each the 

 author's name, and the title and date of the publication in which 

 it appeared, with the addition of at least one reference to some 

 easily accessible illustrated work. Somewhat more is added 

 where difficulty more or less obvious exists. Novelties in 

 nomenclature have been shunned. Except when actually wrong, 

 authors have been left to their own mode of sj>elling, with a 

 general impression that, as in the instance of the word Gastero- 

 pod, it is a little presumptuous to correct Cuvier when backed 

 by Homer in declining yatr-rjp. Subgenera have been very 

 sparingly introduced, and the writer has abstained as much as 

 possible from manufacturing species out of those trifling varia- 

 tions to which every living creature is subject. 



Two lists of the Mollusca of Madeira have been already 

 published : the one of McAndrew, presenting iu his Report to 

 the British Association of 1850 the results of his collecting and 



* Gould, Inverteb. of Massachusetts, 2nd. ed. p. 33, fig. 360. 

 t Tryon, Anier. Mar. Conch, p. 131 , figs. 292 to 294. 



