22 6 Proceedings of the Royal Irish Academy. 



The ruollusean fauna of the Clew Bay area is devoid of any very striking 

 characteristic. Almost all of the principal groups and genera are well repre- 

 sented in its total of 246 species in which the Gasteropods stand to the 

 Pelecypods as 147 to S6. Some of the leading genera, taking them in the 

 wide Jeffreysian sense, appear, indeed, to he more fully represented in Clew 

 Bay than in other Irish West Coast areas. Thus, Odostomia has 20 species. 

 Trochus 9, Venus, Tellina, and Chiton 7 each, while Bissoa with 16 species is 

 equalled only in Miss Warren's list for Killala Bay. Iu one group, however, 

 the Xudibranchs, the Clew Bay molluscan faima with but 16 species compares 

 very luifavourably with that of a neighbouring West Coast area, Ballinakill and 

 Bofin Harbours, where the labours of a skilful observer, Mr. G. P. Farran, have 

 resulted in the discovery of no less than 46 species (" Irish Fisheries Eeport," 

 loc. cit.). There is good reason to believe that a further exploration of some 

 of the outer islands along the Westport Channel, especially Inishimmel (locally 

 known as Iniskiwel), would add considerably to the Xudibranch fauna of 

 Clew Bay. 



Although considered as a section of the Irish West Coast, the Clew Bay 

 area cannot be said to possess any very distinctive character in its molluscan 

 fauna ; the local distribution of the species presents some features of interest. 

 Adopting a rough division of the area into western, middle, and eastern, we 

 find that the total molluscan fauna of 246 species is thus distributed. The 

 western division, including the shores of Clare Island and the waters imme- 

 diately adjacent to a depth of 10 fathoms, yields 155 species, reduced to 105 if 

 the seaward limit be drawn at the 5-fathom line, or to 51 species, or less than 

 half that number, if its area be restricted to the shores of the island between 

 tide-marks. The eastern division, including the shores of the bay from Old 

 Head to Aehill Sound, with the archipelago of drift islands and the shallow 

 channels between them, has a fauna of 145 species, reduced to 53 if we limit 

 the area to the shores between tide-marks ; and the middle section, or the 

 open waters of the bay lying between the eastern and western divisions, has 

 a fauna of 178 species. 



The middle or deeper-water area has the largest number 41) of peculiar 

 species, that is to say, species not found in either of the other divisions : the 

 western has the smallest number 17 of such species, and the eastern division 

 stands intermediate, with 22 peculiar species. Common to all three divisions 

 are SI species, or slightly less than one-third of the total molluscan fauna. 



A comparison of the littoral molluscan faunas of the eastern and western 

 divisions, using the word "littoral'' here, not in its strict sense, but as including 

 all species actually found living between tide-marks during the course of the 

 survey, shows the eastern fauna to be more austral in character than the 



