WOOD, PHYLOGENY OF CERTAIN CERITHIIDM 49 



sub-sutiiral spiral on the later part of the body volution of C. cequispirale 

 suggests the Vulgocerithium group. The species may well be a type from 

 which the C. tuberosum group arose, but Vulgocerithium probably arose 

 from the ancestor of C. cequispirale, C. cornuelianum. 



The young stages of C. cequispirale are unfortunately missing, but the 

 adult shell is so similar in general character to C. lamellosum that the 

 young stages may also have been similar, although this is not certain to 

 be true, for similarity in adults does not necessarily mean similarity in 

 the young. 



Cerithium lamellosum Bruguiere 

 Plate III, figs. 7, 8 ; plate iv, fig. 8 ; plate v, figs. 7, 8 ; plate vi, fig. 6. 



1792. Cerithium lamellosum Bruguiere, Eneycl. Method., p. 488. 



1824. Cerithium lamellosum Deshayes, Desc. des coquilles foss. des environs 



de Paris, p. 370, pi. 64, figs. 8. 9. 

 1866. Cerithium lamellosum Deshayes, Desc. des animaux sans vert, decou- 



verts dans le bassin de Paris, III, 159. 

 1906. Ptijehocerithium lamellosum Cossmann, Essais de Pal^oconch. Comp., 



VII, 81. 



Measurements : Length, 48.4 mm. ; greatest diameter, 13.8 mm. ; apical 

 angle, 29°, changing to 18° on the eleventh volution; sutural angle, 84°. 



The volutions of this species embrace but slightly, producing a long, 

 slender shell. The general outline of the whorls is gently rounded, with 

 slightly impressed sutures. 



The early stages of growth are best seen on a young individual of nine 

 volutions. The beginning of the protoconch of this specimen is not 

 preserved, but it seems to have comprised about one and one-half volu- 

 tions. Beyond this a spiral appears at about the middle of the whorl, 

 the portions above and below the spiral becoming flattened until a dis- 

 tinct shoulder is produced. On the second volution beyond the proto- 

 conch the spiral has become elevated at regular intervals to form faint 

 nodes, and on the third volution another spiral appears below the first, 

 while the nodes are elongated into faint ribs. The second spiral soon 

 becomes as strong as the first, and the two form a slight projection 

 around the median portion of the whorl. The two equal spirals remain 

 stronger than the others throughout the life of the animal, but the shoul- 

 der is never a conspicuous feature of the ornamentation. On the suc- 

 ceeding volution, the fourth beyond the protoconch, there is a faint con- 

 striction of the shell below the suture, which, with the suture itself, out- 

 lines an indistinct spiral. The two volutions which follow are like the 



