120 Mr. Jeffreys on British Mollusca. 



"With respect to the operations of my old friend and partner, 

 Mr. Barlee, in the " ultima Thule," I regret to say that they have 

 not this year been so successful as heretofore. With a view to 

 greater results (the expenses being also much greater), we took 

 into the firm Mr. Damon, the well-known and enterprising shell- 

 dealer, who was to have the duplicates ; but I fear his share of 

 the spoil will much exceed ours. Terebratula cranium, Cerithium 

 metula, Mangelia nana, Aporrhais pes-carbonis, Trochus alabas- 

 trum, and Tellina balaustina (all of them northern treasures) 

 may be enumerated as the chief products of this expedition, so 

 far as it has hitherto proceeded. The variable, and often tem- 

 pestuous, state of the winds and sea, even during the height of 

 summer, will always render the Shetlands an uncertain and un- 

 satisfactory dredging- ground ; although its high northern posi- 

 tion, and the innumerable voes and fiords by which it is inter- 

 sected on every side, afford unusual prospects of rarities, as well 

 as shelter to the molluscous tribe. Mr. Barlee informs me that 

 our dredger, Angus M'Nab, whom he took with him, has been 

 most indefatigable, honest, and intelligent in performing his 

 part of the work. 



A frequent inspection of the cabinet of Mr. M 'Andrew (who 

 has been most liberal in the use of it) has enabled me to correct 

 one or two mistakes which I had made in the identification of 

 Mediterranean and British species, his collection of the former 

 being perhaps unrivalled. It is impossible to define and distin- 

 guish with sufficient accuracy the shells of any isolated district 

 without regard to those of other districts in the same geographical 

 province ; and my recent investigation of the Testacea of the 

 Piedmontese coast satisfied me as to the importance, if not the 

 necessity, of extending the area of observation for the above 

 purpose. Mr. M'Andrew's collection of shells from the coasts 

 of Upper Norway (which is also very rich) was likewise of great 

 service to me; and it confirmed my former opinion, that, in 

 general, the size of specimens increases in a ratio inverse to their 

 northern, and converse to their southern, point of latitude, of 

 which Tellina balaustina, Cardium minimum (Suecicum), Rissoa 

 pulcherrima, Trochus undulatus, and Area raridentata may be 

 cited as examples. Colour appears to depend on different laws, 

 and is generally more vivid in southern than in northern climes ; 

 for instance, Cardium papillosum, Pecten furtivus, and many 

 others. In great depths it is indeed wanting, or nearly so, as 

 may be seen by comparing specimens of Venus ovata and Turri- 

 tella communis obtained from the coralline zone, and a depth of 

 100 fathoms. 



I am indebted to the skilful and experienced pencil of my 

 friend Mr. Alder for figures to illustrate this paper, as well as 



