PLATE 58. 
Page 
Fig. 1-5. Platyceras tenuiliratum. 317 
1. A young shell where the second sinus is not developed. 
2 a. A specimen where the second sinus has begun to he developed. 
2 b. View of the aperture and umbilicus of the same. The expanded peristome is broken off, 
except a small portion adjacent to the volution. 
3 a. Profile of a specimen which is more coarsely striated than usual. 
3 b. Spire of the same. 
3 c. Enlargement of the surface of this specimen, showing the transverse and longitudinal 
striae. 
4 a. View of the spire of an individual where the peristome has been much expanded on the 
side of the volutions. 
4 b. Lower side of the same, showing the umbilicus. The peristome has originally extended 
much farther, so as nearly to cover the umbilicus. 
5 «. A large individual of this species, showing the broad shallow sinus in the peristome. 
5 b. 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 striae have be¬ 
come lamellose. 
Platyceras bisinuatum. 318 
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 appearance 
of the notch in the peristome at this point. 
b. 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. Platyceras pentalobus. 319 
7 a. View of the spire and the plications of the surface. 
7 b. View of the aperture and lower part of the spire. 
7 c. Profile or dorsal view. 
Fig. 8 & 9. Platyceras multisinuatuivi. 319 
8 ft. 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 b. 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. 
9 ft. An older specimen in which the inequalities from the upper part of the last volution are 
worn off, the plications being more strongly marked on the peristome. 
9 b. Dorsal or profile view, showing the outer volution above the apex of the spire. The deep 
sinus in the anterior margin of the younger 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. Platyceras retrorsum. 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. Platyceras intermedium. 321 
o 
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. Platyceras - sp.? 
12 a, b. Two views of a cast : species undetermined. 
Fig. 6. 
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