WOOD, PHYLOGENY OF CERTAIX CERITHIIDM 3r, 



species is made to include many synonyms and a large number of varie- 

 ties, some of which, with a more detailed study of the shells, may prove 

 to be distinct species. 



The close similarity of the young stages of this shell to those of Cerith- 

 ium tuberosum has already been referred to, but the very considerable 

 divergence at an early period of the ontogeny entitles it to rank as a dis- 

 tinct, though closely related, genus. 



Vulgocerithium breve sp. nov. 



Measurements : Length, 34.1 mm. ; greatest diameter, 15 mm. ; apical angle, 

 43°, changing to 25.5° on the last two volutious ; sutural angle, 76.2°. 



Color: Grayish white, mottled with dark brown. Bands of dark brown 

 occupy the depressions between the spirals. 



The apex of this shell is much worn. The youngest volution to show 

 the surface ornamentation is 2 mm. in diameter and has the two strong 

 spirals, as in the young of V. vulgatum. At this stage intercalated spirals 

 are present, both between the primary spirals, on the shoulder and on 

 the lower slopes of the volutions. On the sixth volution of those pre- 

 served the ribs become especially prominent at the level of the upper 

 primary spiral, and a sub-sutural row of nodes is also developed. On the 

 whorl before the last the center of the rib becomes very prominent, and 

 on its lower slope the spirals have a tendency to coalesce and become flat- 

 tened, but this tendency is never carried very far on this species. On the 

 body volution the ribs become weaker and the sub-sutural row of nodes 

 stronger, until the two are of about equal strength. 



The aperture is broadly oval, and the callus of the inner lip is thin, with 

 a prominent posterior tooth. The outer lip is slightly flaring and faintly 

 crenulated. The anterior canal is short, with its margin slightly re- 

 curved. 



Horizon and locality : Recent. The specimens in the collection of Colum- 

 bia University were collected by D. M. Sankey in deep water off the mouth of 

 Grand River, northwest Mauritius. 



No. 20138, Columbia University collection. 



Eemarks: The species is distinguished from Vulgocerithium vulgatum 

 by its shorter form, wider apical angle and heavier and more prominent 

 nodes, which make the outline of the volutions sharply angular. The 

 shell is also thicker and the spirals are more rounded than is usual with 

 Y. vulgatum. 



