SCALA (rLESIOACIHSA) CHATAVINI. 557 



whorl being margined l)y a well-marked ridge ; suture rather deep ; spire elon- 

 gate, gradually and regularly diminishing in size upwards to a sharp point ; mouth 

 small, subcircular. 



Dimensions. — L. 1*> mm. B. 6 mm. 



Distribution. — Not known living. 



Fossil: Red Crag: Woodbridge district (})robably Sutton). 



Bemarks. — The specimen here represented is unique and is the one descril^ed 

 by Wood. It came from the AYhincopp Collection and belongs to the York 

 Museum. It Avas at iirst identified with an Eocene shell, S. semicostata, figured by 

 Sowerljy, l)ut this view is not now accepted. Prof. Sacco, regarding it as a new 

 and distinct species, has named it S. {Acrilla) exsemicostata, in which he was 

 followed l)v M. de Boury. The specimen is fragile, quite perfect, and does not 

 seem to me to show anv signs of beinof derivative. 



Sub-r/enus PLESIOACIRSA, de Boury, MS., 1909. 

 Scala (Plesioacirsa) Chatwini, de Boury, MS. Plate XLVIII, figs. 38, 39. 



1872—79. TurriteUa ! penepolaris, S. V. Wood, Mon. Crag Moll., 1st Suppl., p. 53, pi. iv, %. 20, 



1872 ; T. (Mesalia) penepolaris, 2ik1 Suppl., p. 26, pi. ii, fig. 14, 1879. 

 1890. TurriteUa ? penej)olaris, C. Eeid, Plioc. Dep. Brit., p. 260. 



Specific Ghciracters. — Shell imperforate, turreted, subcylindrical, whorls con- 

 tiguous, slightly convex ; spire slender, elongate, gradually but regularly diminish- 

 ing in size upwards ; ornamented by delicate, inconspicuous spiral stride and by 

 faint oblique lines of growth ; suture distinct ; mouth subcircular. 



Dimensions. — L. 20 mm. B. 5 mm. 



IHstribntion. — Not known living. 



Fossil : Coralline Crag : Sutton, Boy ton. Waltonian : Little 

 Oakley. 



Scaldisien : Dutch Ijorings. 



BemarJis. — The worn specimens now figured have been identified with the 

 TurriteUa penepolaris of Wood. M. de Boury referred them, however, to a 

 subgenus Plesioacirsa, asking me to adopt the specific name Chatwini as a 

 compliment to the late Librarian of the Geological Society, whose friendly 

 assistance from time to time w^e have been glad to acknowledge. 



»S'. Chatwini is not unlike a variety of Acirsa decussata from the Italian 

 Pliocene described by Prof. Sacco,^ but M. de Boury considered it to be both 

 generically and specifically distinct from the latter, proposing the name here 



1 Moll. Terr. Terz. Piem., pt ix, p. 93. pi. ii, fig. 104. 



73 



