58 ANNALS NEW YORK ACADEMY OF SCIENCES 



ther from the horizontal. The development of the two shells is quite 

 different, and for this reason they should rank as at least distinct species. 

 By comparing figs. 4, 5 on plate vii, 4, 5 on plate viii, 3, 4 on plate ix 

 with tigs. 6 on plate vii, 6 on plate viii, 5, 6 on plate ix, it will be seen 

 that V. paraUelum acquires its sharp shoulder by developing its median 

 primary spiral and retaining the lowest primary spiral in a subordinate 

 position, while V. houei develops its uppermost primary spiral to form 

 the shoulder angle and the median spiral is reduced to the rank of a 

 secondary spiral, and is finally indistinguishable from them. 



The development of V. paraUelum and V. houei difi^ers so widely from^ 

 that of Ceritliium that they should be referred to a distinct genus, as is 

 here done. A full diagnosis of the genus awaits a more extended study 

 of related species which should be included in the same genus. The two' 

 species are described here to illustrate the case of parallelism mentioned 

 in the introduction. 



Vicinocerithium bouei (Deshayes) 



Plate VII, fig. 6 ; plate viii, fig. 6 ; plate ix, figs. 5, 6. 



1824. Cerithiiim houei Deshayes, Desc. des coquilles foss. des environs de 



Paris, II, 347, pi. 52, figs. 9-11. 

 1906. Batillaria bouei Cossmann, Essais de Paleoconch. Comp., VII, 134. 



Measurements : Lengtli, 22 mm. ; greatest diameter, 9.5 mm. ; apical angle^ 

 32° ; sutural angle, 81.5°. 



A portion of the protoconch is preserved on one specimen. It is about 

 .4 mm. in diameter and apparently has the form of the typical Cerithium 

 protoconch. The next volution beyond the protoconch has apparently 

 but one primary spiral, forming a shoulder angle Just above the suture. 

 The third volution has more fine spirals on the shoulder, and both ribs 

 and intercalated spirals appear for the first time on the fifth volution. 

 On the sixth volution two of the primary spirals above the spiral of the 

 shoulder angle become stronger, until on the succeeding volution all three 

 are of equal strength, making the outline of the volution an obtuse angle 

 with sloping upper surface and vertical sides. On the next two volu- 

 tions the uppermost of the three primary spirals becomes stronger, until 

 it forms the margin of an exceedingly sharp shoulder angle. Later the 

 median spiral becomes reduced to the size of a secondary spiral, the lowest 

 primary spiral becomes irregularly undulating, and another imdulating 

 spiral of somewhat less strength is developed just above the suture. 

 These changes produce in the adult stage a volution tbat is almost indis- 

 tinguishable from that of V. paraUelum. 



