BIBLIOGRAPHY. 59 



Exhibits. 



By Mr. J. Laycock : Helix aspersa and Helicella virgata, the latter showing 

 much variation, collected at Southport, Sept. i6th, 1906. 



By Mr. R. Cairns : Acha^ina purpurea and A. variegata, types and varieties. 

 By Mr. R. Standen : Sections of the shells oi Limncea, Fhysa, Claiisilia, Cerion, 

 Sagda, Gibbiis, EdentiiUn >, and Placostylus, cut variously to show the internal 

 structure. 



A series oi species of Opisthostoina was shown as a special exhibit by Messrs. 

 R. Cairns, Edward Collier, B. R. Lucas, and R. Standen ; a total of twenty-two 

 species being exhibited, including O. laidlawi and other recently described forms ; 

 also 0. faiibanki (Cairns Collection). 

 It was decided to hold the following 



Special Exhibits at Future Meetings : 

 April loth, 1907 - - The Genus Helicina and its Allies. 

 May 8th, 1907 - - The Genus Ariophanta. 



June 1 2th, 1907 - - The Family Orthalicidae. 



BIBLIOGRAPHY. 



(limited to works received by the society's librarian). 



"Land and Freshwater Mollusks of Alaska and adjoining regions," by 



W. H. Dall {Harriinan Alaska Expedition, vol. xiii. , first portion) pp. I — 171; 



2 pi., 118 text figs. 



" Like all works emanating from the pen of Dr. Dall this contains a good deal 

 more solid and interesting information than is suggested by the title. It was 

 necessary for its production, on account of the uniformity of the boreal faunas of the 

 northern hemisphere, to examine the entire boreal faunas of North America, Green- 

 land, and the adjacent parts of eastern Siberia. The ' general discussion and 

 results' of this investigation are compacted into the first seventeen pages, and 

 include three extremely valuable tables, viz. : — ' I. Distribution of Freshwater Shells 

 north of latitude 49°, according to the drainage systems now existing;' 'II. Dis- 

 tribution of American Land Shells north of latitude 49°;' and " III. Distribution of 

 north-east Asiatic Land and Freshwater Shells.' The rest of the work is devoted 

 to a ' Systematic Catalogue of I^and and Freshwater Mollusks 01 North America 

 from the region north of the forty-ninth parallel.' This area is, of course, sj'nony- 

 mous with almost the whole of Canada and all Alaska. While vast territories 

 therein are only partially or imperfectly explored for mollusks, portions of them are, 

 nevertheless, tolerably well-known and the uniformity imposed on the fauna by its 

 high northern position and unvaried conditions leads to the belief that while much 

 is )ot to be gathered in tracing out the details of distribution many new additions, 

 save, perhaps, among the minuter forms are not to be expected. Altogether 214 

 species, with several varieties are, named in the tables for this area, described in the 

 text and many of them figured. Only forty-eight of these are marked as occurring 

 in Alaska though Dr. Dall later on states that sixty-five species occur in that area. 

 This Alaskan fauna is composite. The fauna of boreal Canada is extended to the 

 north-west, north of the Alaskan range to Bering Sea and the Arctic coast. The 

 fauna of the Pacific slope extends into Alaska south of the Alaskan range. A few 

 species came from eastern Siberia while the remainder belong to the Holarctic, or 

 circumboreal, group. In the systematic part the author has treated certain genera, 

 such as Limmea and Planorbis, monf)graphically, proposing new subdivisions, some 



