558 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.49. 



In the instances when I was able to detect it the color was invariably- 

 reddish brown. Instead of the bulbous, slightly irregular nucleus 

 noted in Nucella, Thais hiserialis has a regular, somewhat dome- 

 shaped nuclear spire, with very minute apical portion and two and 

 a half regularly coUed smooth whorls. Patellijmrpura imtula has 

 the nuclear spire elevated and trochiform, the apex very minute 

 and whitish, the remainder dark reddish brown, smooth and polished; 

 in all about four and a half whorls. T. columellaris, though not so 

 weU preserved, seems to have a similar nucleus. In all cases the 

 transition between the nucleus and the adolescent sculpture is 

 abrupt. 



The sculpture in Nucella may be axial or spiral or both. It may 

 be entirely obsolete over the greater part of the shell, but no matter 

 how smooth the latter appears there are always traces of the spiral 

 ridges which immediately follow the smooth nuclear portion, pro- 

 vided the apical part of the specimen is not worn. 



The spiral ridges of the nepionic sheU between the sutures are 

 persistent in sculptured specimens. They increase by intercalation, 

 and the number of major ridges is quite constant in each species; 

 the differences arising largely from the close or lax coiling of the 

 whorls, which may sometimes leave exposed ridges which are usually 

 hidden under the suture. Between the major ridges there are 

 frequently numerous minor threads which are irregular in number 

 and strength. In rare cases one or more major ridges will split into 

 two or more small ones, which do not materially differ from the 

 minor threads in size or appearance, but usually the discrimination 

 between the two classes is not difficult. 



Beside the regular threads on N. lamellosa there are fine, almost 

 microscopic, more or less obsolete spiral striations, which are hardly 

 perceptible except in specimens entirely free from surface erosion. 



In one variety of N. canaliculata the major spirals are, as it were, 

 flattened down until the interspaces are reduced to sharply incised 

 lines, and the shell exhibits a very marked contrast to the variety 

 with elevated ridges and channeled interspaces which Middendorff 

 named decemcostata. But there are intermediate variations. 



In some mutations, whUe one or two major spirals persist near the 

 periphery of the whorls, the space between them and the preceding 

 suture will be flattened, giving a conical aspect to the whorls. In 

 others the spiral sculpture, after the first nepionic turn or two, may 

 have become quite obsolete, the whorls inflated, and the sutures deep, 

 giving the shell the aspect of a Chri/sodomus. The axial sculpture 

 in lamellosa usually takes the form of elevated sharp lamellae crenu- 

 lated by their intersection with the major spirals. In some cases the 

 lamellae are low except where they cross the spirals, and in a few 

 instances they may take the form of fine low close imbrications such 

 as characterize the form imbricata of the Atlantic N. lapiUus. 



