PLATE 58. 



Puge 



Fig. 1 - 5. Platycebas tenuilibatum. 317 



1. A young shell where the second sinus is not developed. 

 2 a. A specimen where the second sinus lias begun to be developed. 



2 6. Yiew of the aperture and umbilicus of the same. The expanded peristome is broken off, 



e.xccpt a small portion adjacent to the volution. 



;> a. Profile of a specimen which is more coarsely striated than usual. 



3 b. Spire of the same. 



o c. Enlargement of the surface of this specimen, showing the transverse and longitudinal 

 stria; . 



4 a. "View of the spire of an individual where the peristome has been much expanded on the 



side of the volutions. 



4 6, Lower side of the same, shownig the umbilicus. The ])eristomc has originally extended 



much farther, so as nearly to cover the umbilicus. 



5 o. A large individual of this species, showing the broad shallow sinus in the peristome. 

 5 6. View of the same, showing the sinus on the lower side of the shell. 



5 c. An enlargement of the surface near the aperture, where the transverse strljc have lie- 



comc lamellose. 



Fig. 6. Platycebas bisinuatltm. 318 



6 a. The upper side of the spire, showing the sinus in the peristome, and the sinus bordering 



the dorsal lobe : the extension of the latter, being broken off, presents the appoarance 

 of the notch in the peristome at this point. 



6 A. The lower side, showing the sinus on the lower side of the dorsal lobe. The notch in the 



peristome is exaggerated by the broken condition of the shell. 



Fig. 7. Platycebas pentalobits. 319 



7 a. View of the spire and the plications of the surface. 

 7 6. View of the aperture and lower part of the spire. 



7 c. Profile or dorsal view. 



Fig. 8 & 9. Platycebas mpltisinuatum. 319 



8 a. View of the aperture and lower side of the shell (which is represented as too smooth In 



the figure, from a little adhering stone). 



8 6. View of the spire and upper side of the volutions, showing the folds or carina. 



8 c. An oblique view, showing the sinuosity in the anterior margin of the aperture. 



i) a. An older specimen In which the inequalities from the upper part of the last volution are 

 worn off, the plications i)eing more strongly marked on the peristome. 



6. Dorsal or profile view, showing the outer volution above the apex of the spire. Tlie deep 

 sinus in the anterior margin of the yonnger shell is not conspicuous in this one, the peri- 

 stome having become strongly and almost regularly plicate, except on the posterior side, 

 where there is a broad shallow sinus. 



Fig. 10. Platycebas eetroesum. 320 



10 a. The upper side of the spire, from which the shell is worn smooth and partially removed. 

 10 b. Profile view, showing the dorsal side and the elevated apex of the spire. 

 10 c. An imperfect specimen, which may be the young of the same. 



Fig. 11. Platycebas intebmedium. 321 



11. View of the upper side of the spire, which is incorrectly represented at the apex. The 

 apparent contraction toward the anterior side of the aperture is due to accident. 



Fig. 12. Platycebas sp.? 



12 o, b. Two views of a cast ; species undetermined. 



