PIIYLOGENY OF FUSUS AND ITS ALLIES. 4 1 



This is one of the larg^cst and most stately species of the genus. 

 It appears to be a cHrect descendant of F. nodosoplicatus. The spire 

 is elongate and slender, from the drawn-out manner of coiling. The 

 first four or five whorls are round and furnished with round ribs, 

 crossed by strong spirals. This stage agrees essentially with F. 

 fiirriciilus, and with the young of F. toreuiitns, F. tubcrculatns and F. 

 nodosoplicatus. It occurs as slender as the most slender of these, and 

 its genetic relation to these species can not be questioned. The later 

 of these tiirricidns whorls assume a subdued bicarinate aspect, similar 

 to that found in F. tubercniatiis. These whorls are soon succeeded by 

 angular unicarinate whorls, on which a flat shoulder and a nodulated 

 keel are developed. The ribs soon disappear, but the tubercles remain 

 and increase in strength. They finally assume the character of rounded 

 bosses which give a strong undulatory character to the keel. 



Intercalated spirals appear very early, while the whorls arj still round. 

 In accelerated individuals the tubercles become obsolescent on the last 

 whorl, and in some cases disappear almost entirely. The angulation 

 also disappears in many cases, leaving a round ribless whorl. This is 

 most frequently seen in old age individuals, w^here it is associated with 

 other senile features, such as the separation of the inner lip from the 

 columella, the increase in strength of the posterior canal, and others. 



A unique specimen of this species is in the collection of the United 

 States National Museum (cat. 73156). In this shell the turriculns 

 stage continues to the tenth whorl. While the very youngest stages 

 agree with F. turriculns, the succeeding differ to some extent. In ad- 

 dition to producing a more slender spire, they have broader, more 

 elevated and rounded ribs. The interspaces are scarcely half as wide as 

 the ribs, while in F. turriculns the ribs and interspaces are about equal. 

 After the tenth whorl an angulation appears, and the ribs become 

 obsolescent, but tubercles are retained to the end, and these alone mark 

 the last three whorls. They are, however, not so prominent as are 

 those of typical shells. The shoulder is very flat in the last two 

 whorls, being even slightly concave towards the suture. The suture 

 is always marked by a subsutural concavity, and a strong revolving 

 subsutural band indicates a well-developed posterior canal. The final 

 portion of the last whorl show^s old age features, having lost the 

 tubercles. Length of shell, 7^4 inches. It consists of abmit thirteen 

 volutions. 



A large specimen in the same collection (/S//), which must have 

 been almost eleven inches long, has the last six whorls angulated. After 

 completing two of these volutions the ribs have disappeared, and then 

 for nearly four volutic^ns the flat shoulder, strongly noduled keel, 

 subsutural band and relatively simple spirals characterize the shell. 

 Old age characteristics are shown on the last portion of the last whorl. 



