30. PHYLOGENY OF FUSUS AND ITS ALLIES. 



Tryon (Man., v. Ill, p. 63) says of this species: "This is perhaps, 

 a F. coins without carina or a F. ttirriaila without ribs on the body- 

 whorl." It is evident however that this is a distinct species occupying 

 a definite place in the series. 



Atavism occasionally occurs in this species, in the appearance of 

 ribs of the turriculus type on the last whorl. There are seldom more 

 than one or two of these. 



Localities: Mauritius (M. C. Z. 906) ; Indian Ocean (B. S. 6080) ; 

 Ceylon (Phil. Acad. Nat. Sci., n. sp. ?). 



The interrelations of the species of this series may be summed up as 

 given in the preceding diagram. 



3. FUSUS TUBERCULATUS AND ITS ALLIES. 

 FUSUS TUBERCULATUS Lamarck. 



(Plate III, figs. 2, 3, 9.) 



1822. Fusiis tubcrculatiis Lamarck, An. sans. Vert., ist ed., t. VII, p. 123, no. 4. 



1842. Fusus tubcrculatus Kiener, Iconographie, p. 9, pi. VIII, fig. i. 



1843. Fusus tubercidatus Lamarck, Desh. ed., t. IX, p. 444. 

 1847. Fusus, tubcrculatus Reeve, Iconica, sp. 38. 



This species is closely related to F. torcuuins, with which it appears 

 to be genetically connected. The earliest conch stage of this species is 

 the turriculus stage, essentially as in F. toreumus. This is succeeded by 

 an angular stage, in which the characters are those of F. toreumus, the 

 shell being much more slender than in the adult. The characteristic 

 features of the species appear in the later neanic and ephebic stages. 



The most characteristic feature of this species is the compressed 

 character of the adult whorls, which gives the shell a broadly turreted 

 appearance. The shoulder of the adult whorls is flat or even gently 

 concave, devoid of ribs and margined by a strongly carinated keel. 

 The beginning of the shouldered condition is variable ; sometimes the 

 early whorls take on an angular appearance, from the development of 

 a strong central spiral ; sometimes two strong spirals appear, causing 

 bicarination. 



In the adult whorls the nodules of the keel are generally compressed 

 vertically, often assuming a spinose appearance. Soinetimes, however, 

 they assume a rounded form, resembling those characteristic of F. 

 undatns. 



In accelerated individuals the tubercles become confluent on the 

 last whorl, producing a smooth keel. This is particularly well shown 

 in a specimen from Indo-Pacific waters (Nat. Mus. 91740). This 

 specimen is broadly turreted and shows a succession of round and 

 ribbed, angular and ribbed, and angular and noduled whorls, each 

 type grading into the other. In the last type the shoulder is very flat, 



I 



