Clare Island Survey — Marine Mollusca. 22 9 



on the west the boreals are a little less than one-sixth of the australs, 

 while in the east they are almost one-third. Dublin has the following 

 11 austral species not hitherto recorded for Clew Bay : — 



Calliostoina granulatum Pleurobranchus mem- Ceratisolen legumen 



Lunatia sordida branaceus Pholas dactyl as 



Turbonilla pusilla Solenocurtus candidus P. Candida 



Bellardiella gracilis S. antiquatus P. parva 



Of these 11 Dublin australs, however, which are apparently absent from 

 Clew Bay, all but one (Pholas parva) range round the south-west and west 

 coasts of Ireland from Cork to Connemara, and 3 are known to extend even 

 as far north as Donegal. It is not unreasonable, then, to assume that further 

 research would reveal the presence of several of these species in Clew Bay. 

 And although a century-long exploration of the Dublin marine area has 

 yielded records for 11 austral species which two seasons' work has failed to 

 detect in Clew Bay, it must be borne in mind that 5 of these 11 australs, 

 those in italics in the above list, are extremely rare in Dublin. 



On the other hand, the Clew Bay area has 4 austral species, Girculus striatus, 

 Modiolus barbatus, Modiolaria costulata and Diplodonta rotundata, which are 

 absent, not merely from Dublin, but from the whole Irish east coast, from 

 Carnsore Point in Wexford to Fair Head in Antrim. And all of these 4 species, 

 in their extra-Britannic range, are much more distinctly southern than the 

 majority of the 11 Dublin australs which are apparently wanting in Clew Bay, 

 though, with one exception, widespread on the Irish west coast. If, from the 

 Irish austral species, as already defined, we select a sub-group of what may 

 be called Pure Australs — that is to say, of species ranging from the British 

 Isles to latitudes south of the Mediterranean, or ranging from the 

 Mediterranean only so far north as southern England, then the Clew Bay 

 area, in the present imperfect state of our knowledge, shows a total of 18 

 such distinctively southern species to but 17 in the very fully explored 

 Dublin area. 



The mere presence of a species or group of species in a given area is in 

 itself an uncertain test of the character of the fauna of that area. We must 

 consider the standing there of each species, whether it be assured or pre- 

 carious ; and looked at from this point of view the austral element in the 

 Dublin marine molluscan fauna will be found to have much less weight than 

 its numbers would seem to entitle it to. Of the 37 Dublin austral species six, 

 Trochochlea lineata, Gibbula magus, Scalaria clathratula, Alvania carinata, 

 Caecum trachea, and Dentalium vulgare, are quite rare there as compared 

 with Clew Bay ; and two others, Alvania cancellata and Erato laevis, though 



B.I. A, PKOC, VOL. XXXI. B 22 



