Clare Island Survey. 



99 







MARINE MOLLUSCA. 



By NATHANIEL COLGAN. 



Read February 27. Published April 14, 1911. 



I. The area defined and described, 

 n. Exploration of the area : 

 («) Shore-collecting, 

 (b) Dredging, 

 in. The Molluscan Fauna : 



(«) Extent, constitution, and local 

 distribution, . 



CONTENTS 







Page 







Page 



1 



ill. 



The Molluscan Fauna — contd. 









(b) Comparison with East 



Coast 



2 





Mollusea, 



8 



3 



IV. 



Arrangement of the list, 



. 10 





V. 



List of Species, 



. 11 



1 



VI. 







• 4 



VII. 







I. The Area defined and described. 



Unlike most marine areas, the area dealt with in the following list admits of 

 very precise definition. It is included within a line drawn from the south- 

 western extremity of Clare Island to the mainland at Emlagh Point and 

 thence continued along the mainland coast by Old Head, Westport Quay, 

 Newport, and Mulranny to the southern entrance of Achill Sound, whence 

 it passes south-west to Clare Island Light-house and follows the eastern 

 and southern coast-lines of the island to the starting-point. The area is, in 

 short, the shores and waters of Clew Bay, having an extension east and west 

 of some 15 miles and north and south of 8 miles. The coast-line, neglecting 

 the minor sinuosities of the remarkably broken eastern shores, measures 

 approximately 55 miles, a length which would be doubled by strictly 

 following these sinuosities, and adding in the shore-lines of the crowded 

 archipelago of drift islands which gives its peculiar character to the bay. 

 The whole area thus defined may be considered a shallow-water one. 

 The deepest dredging made, between Clare Island Light and Achillbeg, 

 hardly exceeded 25 fathoms, while amongst the creeks and channels of the 

 eastern islands and islets the dredgings ranged from 2 to 5 fathoms. The 

 physical character of the shores and of the sea-bottom, regarded as habita- 

 tions for the various tribes of marine mollusea, is sufficiently varied. On 

 the western side of the bay, the shores of Clare Island between tide-marks 

 are almost exclusively rocky or boulder-strewn, the only sandy beach being 

 U.I.A. PROC, vol. xxxi. A 22 



