WOOD, PHYLOGENY OF CERTAIN CERITHIID/E 83 



but they were doubtless simpler than the youngest stage preserved, and 

 were probably not unlike the young specimens referred to C. inabsolu- 

 tum; but if these specimens are correctly idenified, the adult differs from 

 C. a'quispirah in the direction of loss of fine spirals and of the shoulder. 

 C. lamellosum carries this loss of ornament still farther, and the two 

 constitute a lateral branch in the phylogeny of Cerithium. C. calcitra- 

 poides represents another lateral branch, having its young stages like the 

 adult C. cornuelianum, but its later stages have a shoulder with a sharp 

 angle of the type seen on recent species of the genus. 



As stated above, the European Miocenic and Pliocenic furnisli no un- 

 doubted species of Cerithium sens, str., but in the Miocenic of Florida 

 C. chipolanum seems, so far as can be determined from the description 

 and figure, to belong to this genus and to represent a branch in which a 

 comparatively low spire is developed. C. chipolanum is probably an 

 American representative of an undescribed European form which was 

 the ancestor of the somewhat low-spired recent species, such as C. adan- 

 soni, C. echinatum, etcetera. 



The Pliocenic C. callisoma has the high spire characteristic of the type 

 of the genus C. tuberosum, and it, too, probably had its European par- 

 allel, which was the ancestor of C. tuberosum and other high-spired re- 

 lated forms. The abundance of material in the collections of recent 

 shells reveals a great flowering out of the genus in recent time, and how- 

 ever different the appearance of the adult shells, all reveal their common 

 ancestry by a similarity in their young stages, as described above and indi- 

 cated on plate i. 



Among the genera closely related to Cerithium, Vulgocerithium is per- 

 haps the nearest, developing as it does at an early stage the two strong 

 spirals with intercalated spirals, and diverging from the main line of 

 evolution only in the greater development of nodes and in the absence 

 of a sharp shoulder angle in the adult. Species of this genus seem to 

 undergo little change from Oligocenic to recent time, and all the species 

 described are similar in general appearance and differ from one another 

 only in details. 



The genus Potamides is closely related to Cerithium. The type of the 

 genus P. lamarcM develops the bicarinate ornamentation in the same 

 manner as in C. retardatum (plate iii, figs. 9, 10, and plate iv, fig. 9) 

 or other retarded or primitive species of Cerithium, but retains each 

 stage for a greater portion of the spire, or, in other words, its early on- 

 togeny is like that of Cerithium , but more retarded. The adult expresses 

 its divergence from Cerithium by developing nodes as the chief feature of 

 its ornamentation. As pointed out above, Potamides is a more primi- 

 tive genus than Cerithium in its slightly developed canal, in the sim- 



