26 THE NAUTILUS. 



of aperture, measured from back of lip to edge of parietal callous 

 across the lip-notch, more than half the length, while in hirsuta it is 

 less ; parietal tooth not quite joining lip at basal margin ; internal 

 tubercle short and completely covered by the lip so that it is not 

 visible through the base of the shell. The parietal tooth is con- 

 nected to the end of the lip by a slight buttress and there is a well 

 developed tooth-like process on the lip, but these characters are 

 common to most of the species of this group. Color and hairs about 

 the same as in hirsuta. 



The outline figures bring out the differences better than the de- 

 scription, decepta being drawn from the type and hirsuta from a 

 Blount Springs shell. 



Type : Greater diam. 7, lesser 6^, alt. 4| mm., whorls 5. 



Greater diam. 6^, lesser 5f , alt. 4^ mm., whorls 4§. 



These measurements show the extreme variation in size. 



Type No. 5223 of my collection and cotypes in the collections of 

 the Academy of Natural Sciences, Bryant Walker and T. H. 

 Aldrich. 



In the character and shape of the lip-notch this species bears a 

 strong resemblance to P. pilula Pils. but differs in other important 

 points. 



NOTE ON A VARIETY OF CKEPIDTJLA NIVEA C. B. ADAMS, FROM SAN 

 PEDRO, CALIFORNIA. 



BY W. II. DALL. 



I have recently received from several Pacific coast correspondents 

 a curious form of Crepidula nivea C. B. Adams, the form which on 

 that coast takes the place in the fauna occupied by C. plana Say, on 

 the Atlantic shores, and usually occupies a situs on the interior of 

 dead, univalve shells, especially such forms as Lunatia ; but is some- 

 times found between dead, but still paired, bivalves, or in the borings 

 of Lithophaga or Pholas. It has as many forms as the loci have dif- 

 ferences, but, in general, is externally flat or concave and more or 

 less lamellose, of a white color, and elongate-oval shape. 



The specimens referred to, however, broke all records by being 

 uniformly straight, convex, smooth, equilateral, white and posteriorly 

 attenuated. It was obvious that the uniformity was due to some 

 special situs, but what it was I could not imagine. The other day 



