758 
Transactions of the Society. 
Pleurostomella alternans Schwager, plate XII. fig. 14 a, b. 
Pleurostomella alternans Schwager, 1866, Novara-Exped., 4to, 
Wien, Geol. Theil, vol. ii. p. 238, plate vi. figs. 79, 80. P. 
eocsena , Giimbel, 1868, Abh. k. bay. A k. Wiss., vol. x. p. 630, 
plate i. fig. 53. P. Beussi , Bertbebn, 1880, Mem. Soc. geol. France, 
ser. 3, vol. i. No. 5, p. 28, plate i. fig. 10 a, b ; 11, 12. P. alternans 
Brady, 1884, Chall. Kep., vol. ix. p. 412, plate li. figs. 22, 23. 
This form is distinguished from the preceding by the pointed 
extremity ; and it also frequently exhibits a Textularian arrangement 
of the segments at its commencement. This species is the commoner 
of the two found in the Gault of Folkestone, and this fact is also 
noted by M. Bertbelin regarding the French Gault ; be, however, 
found a third form occurring rarely. P. alternans is a well-known 
Tertiary fossil, and is also recorded from the Bed Chalk of Speeton 
(Burrows, Sberborn, and Bailey). It is found in the Folkestone 
Gault in zone i., specimen b, frequent; zone ii., specimen a, very 
rare ; zone v., very rare ; zone xi., 55 ft. from the top, very rare ; 
50 ft., very rare ; 40 ft., rare ; 25 ft., very common ; 20 ft., common ; 
12 ft., frequent. 
Erratum . — In Part II. of this paper, ante, p. 324, line 2, strike out the words 
“and Wealden beds.” 
