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THE LAND AND FRESHWATER MOLLUSCA OF AUDRUICQ, 

 PAS-DE-CALAIS. 



By JNO. W. TAYLOR, M.Sc. 



(Read before the Society, October 13th, 1917)- 



Lieut. C. Theodore Cribb, who was stationed at Audruicq, near 

 St. Omer, during 1916, availed himself of his scanty opportunities to 

 make a collection of the moUusks to be found within a radius of four 

 or five miles of that place ; these results being supplemented by an 

 occasional visit to Calais. 



The district around Audruicq — embracing Henuin, Ostove, Polin- 

 cove, Zutkerque, etc., all within the arrondissement of St. Omer, and 

 included in the old and comparatively uninteresting province of 

 Picardy — resembles Lincolnshire in being flat and monotonous and 

 intersected with many ditches and dykes ; the only wooded portion 

 occupied the crest of a range of hills five miles away, was composed 

 chiefly of pines, silver birch and heather, and no moUusks whatever 

 were found therein. The total absence of loose stone walls was a 

 deprivation of another fruitful field of investigation. There is no 

 limestone whatever, which may account tor the tenuity of many of 

 the shells and the absence of others from the list, but renders the 

 more remarkable the unusually thickened calcareous apertures of some 

 of the freshwater species. 



There were no small streams, and the river-bed was purely sandy 

 and very unstable, but furnished no moUusks. 



In 1838 Bouchard-Chantereaux published an excellent treatise upon 

 the moUusks of the Pas-de-Calais, the only one ever published for this 

 department, in which he enumerated 102 species, but after deducting 

 those species which are halophilous and others which are now 

 regarded as varieties, this number may be reduced to 85. 



Lieut. Cribb found 55 species, which must be regarded as a 

 gratifying result, more especially as six species are additional to those 

 cited by Bouchard-Chantereaux. 



Twenty-four species of land shells were found, two of which are 

 additions to Bouchard-Chantereaux's Catalogue. 



Arion ater (L.). — The type form of this species was rare about 

 Audruicq, but the fuscous form, var. brunnea Roebuck is widely dis- 

 tributed and common. 



Bouchard-Chantereaux cites Arion ater and nine varieties. He 

 also enumerates Arion hortensis and Arion flavus= Arion intermedins. 



Limax maximus L. — Several shells of this species are in the 

 collection from animals found at Polincove in July. The shells all 

 have well marked growth lines and clearly show that L. maximus is 

 derived from an ancestor with a spirally coiled dextral shell. 



