Yorkshire Naturalists at Bridlington. 215 



the geologists were practically able to make a complete examina- 

 tion of the coast line of the headland from Bempton to Brid- 

 lington. At Thornwick Bay, Selwicks Bay, and near the 

 lighthouse, many interesting effects of marine and subaerial 

 erosion were clearly shewn, and near Thornwick Bay Mr. 

 Stather pointed out a small decapitated valley, now dry, the 

 head of which had been carried away through the falling in of 

 a cave, now a small bay. The well-known buried cliff at 

 Sewerby was seen to advantage, and a little further east the 

 ' sponge-bed,' with its wealth of fossils, delighted the younger 

 students. South of Bridlington the finely-laminated clays 

 were seen to advantage, recent falls in the cliff shewing many 

 fine sections. The beds were carefully examined in the light 

 of the recent works of Swedish geologists in similar series, but 

 no definite data could be gathered in the Bridlington sections. 

 The beach and cliffs yielded many interesting erratics to some 

 members who were beginning to take an interest in the study 

 of geology. 



CoNCHOLOGY. — Mr. J. W. Taylor writes : — Ther^ are 

 sixty-two species of Mollusca already known to live in this 

 district, of which twenty-five are fresh-water shells ; twenty- 

 nine land shells, and eight slugs, with very many well-marked 

 and distinct varieties, but these I should imagine, are very 

 far from exhausting the possibilities of the area in this 

 direction. 



Of the twenty-nine species of land shells, perhaps the most 

 interesting is Azeca tridens, which has only been found at 

 Danes' Dyke on one occasion ; the interest of the other species 

 lies chiefly in the varietal forms assumed under the different 

 conditions to "\vhich they are or have been exposed. 



Particular mention may be made of the primrose-coloured 

 form of Helix aspersa, known by the name of var. exalbida ; 

 the beautiful trellised form, known as var. clathrata ; the 

 five-banded form, var. zonata ; and the one in which all definite 

 markings are obliterated, known as var. unicolor. 



Helix nemoralis also present some remarkable differences 

 to the ordinary shells ; the var. jascialha is especially note- 

 worthy as exhibiting the evidences of a former scheme of 

 coloration, recalling by its arrangement, the species of the 

 genus CampylcBa, which are now chiefly restricted to the 

 mountains of South and South-Eastern Europe, and reminis- 

 cent of the generalized type formerly existent. 



The albino form, var. albolabiata, which is found within a 

 very restricted area on the Flamborough road, displays with 

 the albino forms of Helix aspersa and Helix rufescens, the 

 wonderful effects of food or other life conditions in modifying 

 in the same direction, several distinct and only distantly related 

 species, and is a subject worthy of serious investigation. 



1912 July I. 



