24 PHYLOGENY OF FUSUS AND ITS ALLIES. 



riciilus type. The preephebic characters appear to be those of an adult 

 F. titrriculus, while the ephebic characters consist chiefly in a strongly 

 developed keel, which is at first nodulated, but appears to lose these 

 nodes on the latter portion of the last whorl. If this diagnosis is 

 correct we have here another lateral branch from the F. turricidus 

 stock, in which the angulation, developed to a slight degree in many 

 specimens of F. turricidus, becomes a permanent adult characteristic 

 of specific value. 



Habitat: Eastern seas (Adams and Reeve). 



FUSUS TOREUMUS Martyn. 



(Plate II, fig. 7.) 



1784. Martyn, Univ. Conch., t. 56. 



1843. Fusus toreuma Lamarck, Anim. sans Vert. (Desh. edit.), vol. IX, p. 444. 



1847. Fusus toreuma Reeve, Iconica, sp. 27. 



This species begins with a well-developed tiirriculus stage, in which 

 the whorls are round, furnished with strong rounded ribs and orna- 

 mented by strong and regular spirals. In a specimen in the Boston 

 Society of Natural History collection there are seven round turriculns 

 whorls, before the angulation begins. Usually the specimens of this 

 species are more accelerated, which is shown by the fact that the 

 turriculns stage is restricted to a few only of the apical whorls. In the 

 specimen mentioned intercalated spirals appear in the fifth whorl, or 

 before the angulation. Usually they arise with the angulation, which 

 in the majority of cases is in the fifth or sixth whorl. The angula- 

 tion is generally caused by the strengthening of two spirals, thus pro- 

 ducing a bicarinate aspect. When only one spiral is strengthened in 

 the beginning, this may be supplemented by subsequent strengthening 

 of an adjoining spiral, either above or below. Sometimes both upper 

 and lower spirals are strengthened, thus producing a tricarination. 

 Not infrequently, however', in the adult one of the spirals (typically the 

 central one) surpasses the others in strength, thus giving to the 

 tubercles a sharp aspect instead of the blunt appearance produced by 

 the equal development of two or more spirals. 



With the appearance of the angulation the shoulder becomes grad- 

 ually depressed, until it has become quite flat or even somewhat con- 

 cave. Simultaneously with the flattening of the shoulder the ribs 

 become obsolete towards the suture, and finally are represented only by 

 the tubercles, a strong development of which is characteristic of the 

 species. 



Old age is shown in this species either by a return to the normal 

 round-ribbed condition, a clear case of atavism, or by a gradual loss 

 of the tubercles, and the production of a round ribless whorl. In this 

 latter case a slight carination generally precedes the complete loss of 



