36 THE EKL-GRASS SHELL. 



the body whorl has a stout spiral keel, just below the 

 last suture. 



Astyris tubei^osa^ Cpr., tu-ber-o'-sa, has a very 

 small, slender, brownish shell, the lower whorl of 

 which is marked with two rows of minute, whitish 

 tubercles. It is found on the southern coast of Cali- 

 fornia, as are two other species of the same genus, 

 A. ch^ysalloidea^ Cpr., and A. auranticea^ Dall, both 

 of which are of small size. 



The next genus which we will consider is named 

 Nassa. The word literally means a basket for taking 

 fish. Most of the members of this genus have a retic- 

 ulated or checked surface, somewhat like network or 

 the sides of a basket. 



Our largest Basket shell is named Xassa fossata^ 

 Gld., Nas'-sa fos-sa'-ta. An excellent picture of it is 

 given in Fig. 16. The spire is coni- 

 cal, consisting of five or six w^horls, 

 and ends in a pointed apex. The 

 surface of the whole shell is marked 

 by spiral and transverse ridges, the 

 former of which appear also within 

 the outer lip. The thickness of this 

 lip varies much with the age of the 

 animal, as does the callus of enamel 

 which is spread over the columella. 

 This enamel, in mature specimens, is 

 Fig. 16. of a bright orange color, and contrasts 



finely with the light ash color of the general surface 

 of the shell. 



The canal is short and abruptly reflexed, while just 

 above it is a deep ditch or fossa^ showing at once 

 from what the name is derived. The use of the canal 

 seems to be to afford space and protection for a 



