QUANTITATIVE STUDY OF THE EFFECT OF ENVIRON- 

 MENT UPON THE FOUxMS OF NASSA OBSOLETA 

 ANÜ NASSA TlUVITTATA FROM COLD SPRING 

 HARBOR, LONG ISLAND. 



Bv ABIGAIL CAMr DIMON. 



(1) Tntrodiictori/. The aims of this paper are to niake a i]uantitative inqiiiry 

 iuto the effect of" diverse eiiviiontiicntal couditions upoii the form of two gastropod 

 species, Nassa obsoleta aiid Nassa trivittata, from Cold Spring Harbor, Long Island, 

 and also to record the characteristics of their shells and thns to determine the 

 " place inode " for these shells in that locality. The chaiacters selcctcd for 

 measurenient were those described in systematic works as distinguishiug the 

 species as far as those characteristics could be easily dotermined quantitatively. 

 The work was done under the general direction of Dr Charles B. Davenport. 



(2) General Description of Nassa, its ränge and kabits. Xassa. is a genus 

 of piosobranch gastropods coiitaining many species distributed over the whole 

 World, chiefly in shallow water. The individuals are usnally small, with an ovate 

 shcll and a large foot, which is notched behind and carries a homy opercuhim. 

 The two species, Na.ssa obsoleta, Say (Ili/anassa obsoleta, Stiinpson ; Biiccinum 

 obsoletum, Gould), and Nassa tnvittata, Say (Tntia trivittata, Adams; Biiccinum 

 trivittatum, Gould), found commonly at Cold Spring Harbor, are Americtm forms, 

 and with the less common Nassa vibex constitute the oniy recognised littoral 

 species of the genus found on the middle Atlantic coast of tho United States. 

 Both species ränge froni the Gulf of St Lawrence tn I''liiii(ia. \'irrill ("!')) reports 

 N. trivittata as abuiidant at Casco Bay, Maine, and in Vineyard Sound and 

 Buzzard's Bay, and as common along Long Island Sound ; whoreas N. uhsoleta. 

 he reports as very abundant soutli of Cape Cod and more ioral lurtln r iHntli. 

 N. trivittata, thercforc, reaches its maxinunn inimbcrs further nurlh tlian 

 N. obsoleta. Geologically, N. trivittata is oider than N. obsoleta, having been 

 found in the Miocene of Maryland. Virginia and South Carolina, while N. obsoleta 

 has not been reported fiiuii t'urther back th.in the Piiocene. 



