THE NAUTILUS. 



Voi,. XIII. DECEMBER, 1899. No. 8. 



NOTE ON SIGARETUS OLDEOYDII. 



BY W. H. DALL. 



Nearly two years ago (NAUTILUS, December, 1897, p. 86), I de- 

 scribed, from a single specimen obtained in deep water at San Pedro 

 by Mrs. Oldroyd, an interesting shell belonging to the Naticidae. 

 Although of rather naticoid shape, it showed a well-marked fine 

 spiral striation and a flaring umbilicus, recalling S. concavus La- 

 marck, but with a much thinner and more delicate shell and larger 

 umbilicus. Recently Mr. J. S. Arnheim, of San Francisco, dredged 

 in Drake's Bay, Cal., a larger shell which proves to be the adult 

 form of S. oldroydii. In this the Naticoid form has become more 

 pronounced, the umbilicus smaller and narrower, and a basal zone of 

 paler color than the rest is well marked. The shell .continues to be 

 very thin, the soft parts in life cover it almost entirely, though the 

 thin extension of the mantle over the shell contracts greatly when 

 the creature is placed in alcohol. The soft parts and operculum are 

 typically Sigaretoid, but the shell when adult might almost be taken 

 for a Lunatia. The dimensions of the adult are alt. 50, max. diam. 

 55 mm. It is almost exactly intermediate, as far as the shell goes, 

 between Slgarelus, Eunaticina and Lunatia. 



