241 



rounded, partitions sunken, flexuous, with a subtuber- 

 cular pellucid elevation in the centre. Minute. Diffused 

 but not common. 



P. CRASSULA. NAUTILUS. C. Mont. Sup. p. 79. t. 

 18. y. 2. Walk. t. 4./. 70. F. p. 2'29.Turt. D. 

 p. 119. D. p. 343. Lin. T. 8. p. 117. Depressed, 

 umbilicated, opaque brown, with numerous close-set 

 joints, shewing part of the interior volution, with nu- 

 merous close-set elevated joints ; sides similar ; mouth 

 a little oblique, scarcely clasping the body and furnished 

 with a syphon. English, very rare. 



P. GUILIELMINCE. Macg. Aberd. p. 315. Orbi- 

 cular, disciform, greyish white, considerably compressed, 

 the sides equally convex, bevelled to a thin subcarinate 

 margin ; the cells of the last whorl about fifteen, elevated, 

 narrow, convex, with the concave interstices transversely 

 sulcated ; the centres elevated ; the end moderately 

 raised, semilunar, convex, with its sides embracing the 

 previous turn. 0,02. Aberdeen. 



P. CRENULATA. Macg. Aberd. p. 316. Roundish, 



discoid, pale bluish grey, the sides somewhat convex, 



the margin rounded, the centres slightly depressed ; the 



rays formed by the cells about twenty, curved, convex, 



K 



