CAUSES OF DWARFING 1069 



peratiire." Excessive temperature also causes dwarfing, for polar 

 species entering waters the temperature of which is higher than 

 their optimum will remain smaller than normal. Thus northern 

 species of Pecten never reach the same size in warmer southern 

 waters. The same rule holds for mammals and birds. The dwarfing 

 of the faunas of the Black and Caspian seas may be in part caused 

 by the extremes of temperature in these waters. 



Variation in the amount of water supplied likewise affects 

 the size of aquatic animals. Thus Semper found, in experiment- 

 ing with Limncca staijualis, that "the smaller the volume of water 

 which fell to the share of each animal the shorter the shell re- 

 mained." (Semper-z|4:7(57.) With the same number of whorls, 

 the average length of shell for a given number of animals in 100 c.c. 

 of water was Y^ inch, while the same number of animals in 2,000 

 c.c. of water had an average shell length of }\ inch. 



Deep-water individuals are also, as a rule, smaller than the 

 shallow-water forms, various factors, such as difiference in tempera- 

 ture, density and salinity of w^ater, of food supply, etc., being op- 

 erative here. 



The dwarf faunas of the Windsor limestone (Mississippic of 

 Nova Scotia) and of the Magnesian limestone or Zechstein of 

 Europe, is probably due to several causes, notably the decrease 

 in volume of water and the accompanying increase in salinity of 

 the water, these deposits being intercalated between continental 

 sediments. Similar dwarfed faunas are obtained from the Cretacic 

 of New Mexico and southern Colorado. (Stanton-49; Shimer and 

 Blodgett-46:d7.) 



BIBLIOGRAPHY XXIX. 



1. AGASSIZ, ALEXANDER. 1888. Three Cruises of the Blake, 2 vols* 



Bulletin of the Museum of Comparative Zoology, Vols. XIV, XV. 



2. ANDREE, KARL. 1912. Probleme der Ozeanographie in ihrer Bedeut- 



ung fiir die Geologie. Naturwissenschaftliche Wochenschrift, No. 16, 

 pp. 241-251. 



3. BALCH, FRANCIS NOYES. 1901. List of Marine Mollusca of Cold- 



spring Harbor, Long Island, with descriptions of one new Genus and two 

 new Species of Nudibranchs. Proceedings of the Boston Society of 

 Natural History, Vol. XXIX, pp. 133-162, pi. i. 



4. BOURGUIGNAT, J. R. 1890. Histoire Malacologique "du Lac Tangan- 



yika. Annales des Sciences Naturelles, serie 7"^® Tome X. 



5. CHUN, CARL. 1886. Ueber die geographische Verbeitung der pelagisch 



lebenden Seethiere. Zoologischer Anzeiger, Nr. 214, 215. 



6. CLARKE, JOHN M. 1897. The Stratigraphic and Faunal Relations of 



the Oneonta Sandstone and Shales, the Ithaca and Portage Groups in 

 Central New York. Fifteenth Annual Report of the New York State 

 Geologist, pp. 27-82; also, Sixteenth Annual Report, 1898. 



