WOOD, PHYLOGENY OF CERTAIN CERITHIID^ 37 



Vulgocerithium gracile Philippi 



1836. Cerithium gracilis Philippi, Enum. Moll. Sicil., p. 193. 



1887. Cerithium vulgatum Tryon, Manual of Conch., p. 126, pi. 21, fig. 43. 



Measurements : Length, 30.8 mm. ; greatest diameter, 11 mm. ; apical angle, 

 39.5°, changing to 17° on the last three volutions ; sutural angle, 82.5°. 



Color : Yellowish white, mottled with reddish brown, which usually passes 

 in sinuous lines across the spirals. 



The ornamentation is entirely obliterated on four volutions of the best 

 specimen available. The fifth volution has the usual two strong spirals, 

 and there are at this stage three intercalated spirals, with at least four 

 on the shoulder and two on the lower slope of the volution. All the 

 spirals are crossed by ribs, and varices occur to the number of about three 

 to the volution. A similar type of ornamentation persists to the seventh 

 volution. At this stage the spirals are still distinct, and the embracing 

 of the whorls is loose enough to leave a well-marked slope below the lower 

 strong spiral. On the next two volutions the finer spirals gradually 

 coalesce with the coarser ones, which then become broad and flattened. 

 The ribs between the varices become very narrow, and a sub-sutural row 

 of nodes is developed. The adult ornamentation is characterized by 

 numerous narrow ribs projecting in a sharply pointed but not very promi- 

 nent node at the level of the first primary spiral. The slight shoulder is 

 concave and the lower slope of the whorl gently convex. A sub-sutural 

 row of nodes is present on the adult whorls, and a row of fine nodes ap- 

 pears just above the suture. The ribs become nearly obsolete on the body 

 volution, being represented by two rows of nodes. 



The aperture is of the t3'pe usual in this group, with an oval outline, a 

 narrow callus and a posterior tootli. The outer lip is slightly flaring, 

 and the anterior canal is a little longer than in the last species, with a 

 narrow opening and slightly reflexed margin. 



Horizon and locality : Recent. Locality unknown. 

 No. 20139. Columbia University collection. 



Eemarks : The species has been referred to Vulgocerithium, vulgatum, 

 but it is distinguished by its smaller size, proportionally coarser and more 

 rounded spirals and by the more sharply pointed form of the main row 

 of nodes. The spirals below the slight shoulder become rounded and 

 irregularly nodose, instead of flattened and inconspicuous, as in T". vul- 

 gatum. 



The shell bears a close resemblance to the last species described, but it 

 differs in several important respects. The development is much more 

 retarded than that of V. plicatiim. since tlie coalescence of the spirals does 



