508 PROCEEDINGS OF THE ACADEMY OF [Dec, 



well established in the Oligocene. P. micronematica is a much 

 -mailer species than P. decussata (of which it is probably an ancestor), 

 with smaller, very slender primary spirals. In young P. decussata 

 the spirals are much larger and closer together. Both of the speci- 

 i nens found are in the hard tufaceous rock of the Pecten bed. Neither 

 shows the early or embryonic whorls. 



Natica bolus n. sp. PI. XXII, fig. 9. 



The shell is rotund, solid, composed of 4| whorls, the earlier 

 ones slowly, the last two rapidly enlarging. The spire is very low, 

 conic, narrow, and small, suture but little impressed; last whorl 

 is a little depressed below the suture and smooth throughout. The 

 aperture is semicircular as usual. The parietal margin is heavily 

 calloused, chiefly in the upper angle, a short rounded ridge emerg- 

 ing just below it. A larger bluntly triangular lobe projects at the 

 upper edge of the umbilicus, and a less conspicuous pad terminates 

 a cord spirally entering the umbilical cavity. 



Alt. 9, diam. 9.5 mm. 



Gatun bed A. P. B., 1910. 



This species differs from N. canrena by its much less deeply im- 

 pressed suture, absence of tangential plication above, and various 

 details of the columellar region. 



Natica canrena (Linn.). 



Several specimens, the largest having a diameter of 28 mm., 

 were taken by one of us in the Gatun bed. They belong apparently 

 to an early race of the N. canrena stock, such as that occurring in 

 the Bowden bed. No opercula were obtained. 



Natica canalizonalis n. sp. PI. XXII, fig. 10. 



The shell is hemispherical with a very small low-conic, subacute 

 spire of 4^ whorls, the last two rapidly enlarging, last whorl somewhat 

 depressed below the suture, which is very little impressed. The 

 inner lip is very heavily calloused posteriorly, the part above the 

 umbilicus very short, emerging a little, projecting at the upper 

 margin of the umbilicus, the face of the projection transversely 

 dented. The umbilicus is ample, rendered lunate by a flat median 

 callus which terminates a cord spirally entering the umbilicus. 



Alt. 8, diam. 8.3 mm. 



Gatun bed, A. P. B., 1910. 



The ample umbilicus, heavy, transversely dented parietal callus 

 and appressed suture characterize this species, of which only "one 

 specimen was taken. 



