PIIYLOGENY OF FUSUS AND ITS ALLIES. 39 



one above, /. c, below the upper suture, and another one below the 

 main spirals, sometimes exposed, but generally covered by the edge 

 of the succeeding whorl. The whorls follow each other in a close coil, 

 which causes the sutures between them to be but slightly impressed, 

 and gives to the spire a thick-set, less slender and graceful, and more 

 embracing appearance. 



By the end of the first volution of the conch the ribs have become 

 less sharply defined, and the three main spirals have become stronger 

 and sharper, with distinct and relative wide interspaces. Before the 

 end of the second volution of the conch has been reached, the primary 

 spirals have become very sharp on the ribs, and intercalated spirals 

 appear between them. The spiral of the shoulder also becomes 

 more distinct, while at the same time the shoulder takes on a more 

 definite expression. The central one of the three primary spirals forms 

 the shoulder angle. In a \oung specimen (pi. Ill, fig. i) this angu- 

 lation is continued till after the end of the seventh volution, after 

 which, for the next half volution, the angulation becomes less pro- 

 nounced and the ribs, which have been slowly becoming fainter, become 

 obsolete. By the time that the ninth volution is reached, the outline 

 of the whorl is practically a uniform curve, which is, however, slightly 

 disturbed, by a subdued central carina or keel, formed by the strong 

 primary spiral. There are, however, no nodes. The lip is strongly 

 lyrate within, the lira corresponding to the inter-spiral spaces. This 

 variety is comparable to F. longicaudiis-torcumoides of the F. coins 

 series. 



In an adult specimen (pi. Ill, fig. 8) the seventh and eighth 

 volutions are less strongly angulated, the shoulder at the same time 

 being more convex. The undulations of the subsiding ribs, are still 

 faintly visible on some parts of the ninth volution, the shoulder having 

 become so convex as to make a round whorl. Just below the suture, 

 in the last three or four whorls, there is a narrow concavity, due to the 

 formation on these whorls of a pronounced posterior canal. 



The upper one of the three primary spirals is still strong on the 

 ninth volution, thus diminishing the accentuated appearance still made 

 by the central spiral. In the tenth volution the whorl is perfectly 

 rounded, and after the manner of F. dupctit-thouarsii is strongly lined 

 by the spirals. The ribs have completely disappeared, and the upper 

 portion of the whorl has become slightly concave. Intercalation has 

 become highly compound. The secondary spirals have nearly reached 

 the strength of the primary ones, and are evenly spaced with them. 

 Between these stronger spirals are five or more subequal fine revolving 

 lines. Between these, on the final portion of the shell, are still finer 

 ones, making in all from ten to fifteen fine revolving lines between each 

 pair of coarser ones. These latter are themselves covered with from 



