270 PROCEEDINGS OF THE ACADEMY OF [1896. 



Aperture trapezoidal, white within, with livid brown or purplish 

 tracts. Outer lip having a very deep rounded sinus a short dis- 

 tance below the suture, its outer portion then produced forward in 

 a broad rounded lobe, retracted again on the lower outer portion, 

 and produced in a more or less prominent narrow lobe at base. 

 Columella concave ; parietal wall covered by a transparent film, 

 with a slight callus developed near the posterior angle of the aper- 

 ture. 



Alt. 52, diam. 25 mm. Alt. 54, diam. 27 mm. Alt. 53, diam. 

 28 mm. 



Described from four adult and four young specimens in collection 

 of the Academy of Natural Sciences of Philadelphia, and one adult 

 in collection of the United States National Museum. The latter 

 specimen, having suffered least erosion, is figured. 



The peculiar sinuousity of the lip is strictly an adult character. 

 In most specimens it is not perceptible a half whorl back from the 

 lip-edge, although in the last of those measured above, the sigmoid 

 contour is seen in the growth lines almost a full whorl back. Four 

 young specimens examined have the lip hardly more bent than in 

 the ordinary PachycheilL 



The altitude given above is, of course, measured on decollate 

 specimens. A young shell 52 mm. high has 7 whorls left; one 

 measuring 33 mm. high has 7i, and probably has lost about 1^. 



Specimens subsequently received from Dall, collected by Dr. 

 Spear in Tehuantepec, are dark chestnut colored, with traces of 

 darker streaks, and the sinuation of the lip is somewhat less deep 

 than in the types. The columella is brown. One very old speci- 

 men approaches a cylindrical form, measuring, in its truncated con- 

 dition, alt. 51, diam. of last whorl 27, diam. of the truncated top 16 

 mm. Somewhat less than three whorls are left. 



