The Basket Shells. Dog Whelks 



In the aquarium the sole of the foot is often appHed to the 

 surface of the water, the shell hanging downward, a familiar 

 position assumed by certain fresh water snails. 



The Nassas are very tenacious of life. They survive for 

 months enforced hibernation in cabinets and neglected aquarium 

 jars, and revive with no apparent damage when restored to 

 their natural element. 



The basket shells show an astonishing tendency to variation, 

 bringing discouragement and chaos to the systematic student 

 who wishes to draw sharp distinctions between species. About 

 five hundred species have been erected already, three-fourths of 

 which Tryon has reduced to the rank of synonyms. The 

 American species are few. « 



The Channelled Basket Shell (A^. fossaia, Gould) is the 

 largest species in the family. It is one to two inches long. The 

 surface is sculptured with revolving ridges and grooves, which 

 show distinct and white within the wide aperture. Longitudinal 

 grooves cross the whorls, cancellating them finely on the spire, 

 forming strong rounded nodules on the upper half of the body 

 whorl. The exterior is brownish yellow and dull; interior ridged, 

 polished, callous, bright orange. Columella excavated; lip 

 toothed. The umbilicus leads out into a deep channel that winds 

 around the base of the body whorl. 



Habitat. — California. 



The Dog Whelk {N. trivittata, Say), of our Atlantic sea- 

 board is a familiar inhabitant of sandy shores from Maine to 

 Florida. The long spire has close spiral ridges, crossed by 

 stronger, beaded ridges. The sinus, deep between the whorls, 

 bears a strong top row of nodules, tinted pink or yellow, and 

 faintly banded below. 



When the tide goes out these mollusks come quickly up from 

 under the sand, and make for the water, the broad foot holding 

 its forked tail erect, the tentacles waving ahead, and the siphon 

 thrust out of the notch in the shell directly above the head. The 

 shell lies horizontally upon the body; the small operculum is 

 hidden by the spire. Fine dots of purple adorn the colourless 

 body. 



The ■Worn-out Basket Shell (N. ohsoleta, Say) is eroded at 

 the apex — a basket with its bottom badly damaged. This is a 

 dark-coloured Nassa, brown or olive, lightened occasionally by a 



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