360 Mr. H. M^ Andrew on Mr. Jeffreys' s last Dredging Report, 



Of the distributioTi of Isocordia cor our information is im- 

 perfect. The Dublin-Bay specimens are, I believe, the largest. 

 Ihave dredged it in at least two localities in the Hebrides, 

 though only dead in an adult state, my largest examples much 

 below the ordinary dimensions of the species. 



TelUna halaustina is of extreme rarity in the Atlantic, 

 where next to nothing is known of its distribution. Except 

 on our northern coasts, the only Atlantic specimen of which 

 information has reached me is a single valve obtained by my- 

 self, in company with the late Dr. S. P. Woodward, off Cape 

 Finisterre of Spain. In the Mediterranean the size I have 

 found to vary, not from north to south, but from east to west, 

 being smallest in the ^gean and largest at Gibraltar ; so that 

 this species does not throw any light upon the question. 



Tectura virginea is about as large in the Bay of Vigo as in 

 the British seas, much larger than I have procured it from 

 more northern latitudes on the Scandinavian coast. 



Of Defrancia purpurea my finest and largest specimens 

 were obtained at Vigo. 



The foregoing examples (not selected by me, but by Mr. 

 Jeffreys) render it, I conceive, needless for me to bring for- 

 ward any instances in support of my views. I may, however, 

 name a few of the commonest and best-known Mollusca of 

 our shores, as Purpura lapillus^ which I have found largest in 

 the south of England, Mytilus edulis at Algiers, Buccinum 

 undatum in Shetland (frequent in the neighbourhood of the 

 North Cape, where it is much smaller), Fusus antiquus in 

 Liverpool Bay, &c. 



I should not omit mention of two striking exceptions to 

 what I conceive to be the general rule — viz. Haliotis tuhercu- 

 lata and Chiton cajetanus^ both of which attain their largest 

 dimensions in their most northern habitat, the Channel Islands 

 and south coast of Brittany respectively. This I do not pretend 

 to account for. They do not progressively augment in pro- 

 portion to their northern latitude, as I have obtained both 

 species on the north coast of Spain, where they are no larger 

 than in the Mediterranean. Other southern species which 

 find their northern limit on our coasts (e. g. Venus verrucosa j 

 Cytherea cMone^ Cardiu maculeatum^ and C. tuberculatum) are 

 larger in the Mediterranean. I could cite a few exceptional 

 instances of specimens being larger in their southern distribu- 

 tion ; but, to show that there are other conditions besides lati- 

 tude which affect growth, I will mention that the individuals 

 of Chiton fascicularis are uniformly larger at Mogador than I 

 have found them elsewhere, while at no great distance, at 

 Lancerote, they ar^ much smaller than in any locality that I 



