104 BULLETIN 91, UNITED STATES NATIONAL MUSEUM. 



posterior row of tubercles on each turn flesh colored. Nuclear 

 whorls 3^, the first half smooth, the remainder marked by two slender 

 spiral threads, which are placed anterior and posterior to the middle 

 of the whorls, leaving a narrow space between them about one-half 

 the width of that between the summit and the first spiral thread 

 below it. In addition to the spiral threads, these whorls are marked 

 with slender axial riblets, which curve strongly, retractively from the 

 summit to the first spiral thread, crossing the space between the two 

 spiral threads in a straight, retractive line, then continuing over the 

 anterior portion of the wall in a slightly curved, protractive manner. 

 These riblets are very feeble on all but the last nuclear whorl, on 

 which they are much stronger. On this there are 34. Postnuclear 

 whorls flattened. The first four are marked with two strong spiral 

 cords, of which one is immediately below the shouldered summit, 

 while the other is a little above the suture. Beginning with the fifth, 

 a slender spiral cord makes its appearance half way between the other 

 two. This increases rapidly in size and on the seventh is equal to 

 the others. In addition to this spiral structure, the whorls are 

 marked with strong axial ribs, of which 16 occur upon the first, 18 

 upon the second to sixth, 20 upon the seventh to ninth, and 22 upon 

 the penultimate turn. On the first four whorls, the junction of the 

 axial ribs and spiral cords f orm strong, rounded tubercles on the cord 

 at the summit, while at the anterior cord the tubercles are truncated 

 posteriorly and slope gently anteriorly, the whole having a some- 

 what dumbbell shape. On the remaining cords the same structure 

 applies to the shape of the tubercles of the first and third cords, 

 while on the median cord of the fourth and fifth whorls the tubercles 

 are elongate-oval, having their own axes parallel with the spiral 

 sculpture. On the remaining cords, the tubercles and the median 

 cords resemble those of the supraperipheral cord. The spaces 

 inclosed between the spiral cords and the axial ribs are large, well 

 impressed, squarish pits on the first four turns, while on the remain- 

 ing turns they appear as rounded pits. Sutures strongly impressed. 

 Periphery of the last whorl marked by a smooth spiral cord, which is 

 separated from the supraperipheral cord by a groove about as wide 

 as that which separates the supraperipheral cord from its posterior 

 neighbor, and crossed by the continuations of the axial riblets which 

 terminate at the posterior border of the peripheral keel. Base 

 moderately long, well rounded, marked by three, strong, broad, low, 

 rounded, equally spaced, spiral cords, which are separated by narrow, 

 rounded, impressed channels. The last one of these is partly upon 

 the columella. Aperture irregular, decidedly channeled anteriorly; 

 posterior angle obtuse; outer lip rendered sinuous and irregular by 

 the external sculpture; columella covered with a very thick callus 

 which is reflected over the base and extends over the parietal wall. 



