On tie BoriiHi MoUusca of St. Andreios. 3G9 



however, tlie first joint of the antennre, thongli 8tronu;ly 

 swollen, is less elliptical in ontlii.e and more densely greyish 

 jJoUinose, while, inter alid, the aI)doniinal markings are very 

 different from those of //. tuinidicornis and the front tibiie 

 are more slender. As regards the wings, the absence or 

 almost total absence of markings and coloration in the first 

 basal cell and in the first posterior cell with the exception 

 of its distal extremity is highly characteristic, and gives the 

 wings when s.^en against a dark background a longitudinally 

 streaked appearance, reminiscent of that presented by the 

 wings of H. copemawi, Austen, and certain of its allies; 

 with the group represented by H. copemanii, however, the 

 present species has nothing beyond generic characters in 

 common. 



XXXVII. — On the Boring MoUusca of St. Andrews. 

 By B. Lindsay, Gattj Marine Laboratory, St. Andrews. 



[Plate VIII.] 



Professor McIntosh, of St. Andrews, has alwa^'s maintained 

 that the main work of marine boring organisms is accom- 

 plished by mechanical means, and not necessarily by the 

 aid of an acid secretion. The latter theory, however, has 

 been advocated within comparatively recent years, and 

 Professor Mcintosh therefore requested me to make some 

 fresh observations on the subject. No traces of acid 

 secretion were found ; but the details of mechanical boring, 

 on the contrary, were observed, and the descriptions of it 

 given by previous writers were confirmed and extended. 



St. Andrews offers a good field for the study of this 

 subject in its most important aspect— namely, in connection 

 with coast erosion, which is undoubtedly much assisted by 

 the work of marine borers. The types studied were 

 Zirpha'a [Phola^] crispata^ Saxicava vugosa, and Tapes 

 pullastra. 



Of the Boring MoUusca of St. Andrews, Zii-pha'a (PJioIas) 

 crispata is far the most important in numbers and in activity. 

 It removes vast quantities of shale and no inconsiderable 

 amount of sandstone, and is undoubtedly a most imjiortant 

 factor in the process of coast erosion. 



At the East Rocks the boring-grounds of Zirpha^a are two, 

 and each is associated with serious encroachment of the sea. 

 One is situated below a spur of rock whicli protects the bay 



