MARSHALL: ADDITIONS TO "BRITISH CONCHOLOGY." - 187 



of Sars and Jeffreys will at once show the differences between the two. 

 This variety has some resemblance to A. incrassatus var. succisa Jeff., 

 though I consider the latter shell to be distinct from A. iticrassatus. 



A. incrassatus Jeflf. — Between the Orkneys and Slietlands i45f., 

 a single specimen; off the Shetlands inf. and i55f., several; also 

 some valves off the Faroes in 71-85^ (Simpson)! 



A. ferruginosus Forb. — Off Loch Ryan 2 of. 



A. cycladius S. Wood. — Straits of Korea 4if., 32*42 N., i29"49 E. 

 ('Sylvia')! 



Gwyn Jeffreys' original figures in the "Annals " for 1858 are good as 

 outlines, but the dentition is incorrect ; the latter should be as stated 

 in his description.' Each valve has one cardinal tooth and two 

 laterals. 



Scintilla? eddystonia Marsh., " Journ. Malac", 1895, vol. iv., p. 

 35, fig. I. — After much reconsideration and recomparison, I am con- 

 firmed in my opinion as to the specific distinctness of this shell from 

 Diplodonta rohmdata, but think it may be removed from Scintilla 

 and placed in Diplodonta as D. eddystonia. I had already stated 

 that " I have been greatly puzzled where to place this species." I 

 am further convinced that should it prove not to be a true species, it 

 will at any rate not be D. rotundata. To be so, one would have to 

 assume thai D. rotundata in its junior stage can take on two distinct 

 forms, externally and internally, a phenomenon unknown in my ex- 

 perience. It is really nearest to D. trigoniila of the same size, some 

 specimens of which are more transverse or oblique than the type ; 

 but from that S. eddystonia is thinner, the beaks are not so obtuse, 

 and the teeth and hinge-line, though similar, are not nearly so solid 

 nor developed. 



A young specimen of D. rotundata ot the same size as S. eddystonia 

 differs in being much thinner, the beaks less prominent and more 

 equilateral, and the contour roundish instead of oblique. The dentition, 

 though somewhat similar, differs in the cardinals not being nearly so 

 strong and developed, except in specimens six times as large ; they 

 have a different slope, and there is a plate-like lateral on each side of 

 the beaks, whereas in S. eddystonia the lateral is on the posterior side 

 only. It is also significant that none of my specimens of S. eddystonia 

 exceed a line, and they all appear adult so far as one can fairly judge. 

 I am indebted to the Marquis di Monterosato for a graduated series 

 of the young of D. rotundata, and on a comparison it is impossible to 

 assume that the two shells can be the same species ; the differences 

 would strike the most casual observer. 



Searles Wood, in his " Crag Mollusca," says that the young of D. 

 rotimdata of al! sizes are abundant in the Crag deposits, but he does 



I Brit. Conch., vol. ii., p. 228. 



