22 10 Proceedings of the Royal Irish Academy. 



undoubtedly present, if rare, in Clew Bay, rest their claim to a place in the 

 Dublin fauna each on a single old record. And to counterbalance this 

 there are only two of the Clew Bay austral species, C'cdliostoma Montagui and 

 Lunatia catena, which appear to be rarer there than in Dublin. 



Writers on our marine mollusca have more than once drawn attention to 

 the great abundance of Cerithiiun on the west as compared with the east 

 coasts of Ireland. The Clew Bay dredgings gave striking proof of this 

 preponderance, not only in the commoner species, C. reticulatiim, but also in 

 the allied G. pervcrswm. A day's dredging in Dublin waters has never 

 yielded me more than half a dozen shells of either species ; a single haul off 

 Clare Island in July, 1909, gave me 160 perfect and 108 broken shells of the 

 first species, and another haul off the island in July, 1910, gave me 132 perfect 

 shells of the second. In Clew Bay, too, as in the west generally, C. reticidatum 

 attains to a far finer development than in Dublin. Specimens dredged off 

 Scotch Bonnet in 1910 were fully 16 mm. (■§• inch] in length, twice the size of 

 my largest Dublin specimen. 



IV. AlJKANGEMFNT OF THE LlST. 



Iii the following detailed account of the Clew Bay species I have adopted, 

 as the most convenient for students of Irish distribution, the nomenclature 

 and sequence of Mr. A. R. Nichols' well-known List of the Marine Mollusca 

 of Ireland (Proc. R.I.A., 3rd series, vol. v, 1900). Where the generic name 

 of the list differs from that used in Jeffreys' " British Conchology," I have 

 added Jeffreys' generic name in brackets, together with his specific name 

 where that differs in more than grammatical form from the specific name in 

 the List. In most cases it has not been thought necessary to give the depth 

 of the various dredgings in which the species were taken. Only the number 

 of dredgings and their range in depth are given. Thus, " taken in 10 dredgings, 

 2-19 f." indicates that a species was dredged in 2 f. and in 19 f., and in 8 

 other hauls at intermediate depths. As a help in estimating the relative 

 frequency and degree of development of the various species within the area, 

 details are given rather freely as to the number and maximum size of the 

 specimens taken, the measurements being in millimetres of, say, 25 to the 

 English inch. The capital letters, W., M., or E., affixed to the name of a 

 species in the present list, indicate the divisions of the area in which that 

 species was found to occur. The western division, W., includes the shores of 

 Clare Island and the waters within half a mile of them, where several 

 dredgings were made off the harbour and Granuaile's Castle in 5 f., and one 

 off Light-house Cove in 10 f. The eastern division, E., includes all the shores 

 of the mainland from Boonah Quay to the southern opening of Achill Sound, 



