﻿128 SMITHSONIAN MISCELLANEOUS COLLECTIONS [ VOL. 47 



lost. The complete nepionic shell has lost its umbilicus entirely, but 

 has not acquired a canal, which only appears with the formation of 

 the first whorl of the adult shell. The larval shell of Dolium is 

 similar, though larger, and was even described as a species of Helix 

 by C. B. Adams, half a century ago. I cannot help thinking, when 

 we remember how large a proportion of the Tsenioglossa have the 

 aperture unsulcated, that the holostomate character of these larvae is 

 significant and points to the acquirement of a siphonal canal in this 

 group as a case of convergence in development, while the early 

 spirality of the operculum and its subsequent concentric development 

 in Fusitriton show the loss of a character once characteristic of the 

 group and an instance of what might be called negative convergence. 

 The group to which these approximations tend is of course the muri- 

 coid Rhachiglossa with which naturalists long united the tritons. 



We find however that in the completed nepionic shell of forms like 

 T. costatus Born (olearium Auct.) a well-developed sulcus exists, 

 and the whole shell has the appearance of a small, stumpy, horny 

 Astyris. In the single operculum of this stage which I have been 

 able to examine the form was subtriangular, concentric with the 

 nucleus ill-defined and apparently mid-lateral. The larval shell of 

 Septa is identical in general characters but is followed by a neanic 

 stage in which the elegant granular sculpture, and the delicate rose 

 color of the test contrast effectively with the features of the adult, 

 though there is no very pronounced line of demarcation between the 

 two. In all these forms, and the same is probably true of Dolium 

 and its allies, the larval shell is furnished with caducous spiral lines 

 of projecting hairs and under them is smooth and polished, or faintly 

 spirally striated, the height of the spire depending upon the length 

 of time the individual floated about in the larval state before finding 

 itself in a location where it might conveniently settle on the bottom. 

 Sometimes there may be as many as seven whorls. With the begin- 

 ning of the adult type of whorl a lining of shelly matter is deposited 

 on the inside of the horny larval shell. The latter loses first its hairy 

 periostracum, then it may itself disintegrate, leaving the shelly in- 

 ternal cast at the apex of the shell, which is sometimes filled up solid 

 with shelly matter. Sometimes the thin, horny apex of the larval 

 shell in drying may become axially wrinkled, suggesting sculpture, 

 but on wetting the wrinkled part it will usually expand to its normal 

 smooth condition, leading one to reflect how easy it is to make 

 hasty conclusions. 



The verge in this group is usually elongate conic with a groove 

 serving as a conduit, the organ is usually bent backward and often 



