1G4 Proceedings of the Royal Physical Society. 



Platyostomella Scotoburdigalensis — Mheridge, Jun. 

 [PL III, Figs. 1-9.] 



Littorina Scotoburdigalensis. Eth. Jun, Quart. Jour. Geol. Soc.,1878, xxxiv., 

 p. 18, PI. II., Figs. 26, 27. 



S'p. Char. — Shell small, thin, and naticiform in shape, of 

 from 3^ to 4 whirls, the last or body whirl being large and 

 far exceeding the united measurements of the others ; spire 

 short and more or less depressed, but not flattened. Each 

 whirl is somewhat flattened above, near its union with the 

 preceding whirl, the line of separation, or suture, being well 

 marked, and to some extent channelled, the larger the speci- 

 mens the more marked the channelling ; body whirl inflated 

 and somewhat prolonged in the direction of its growth. 

 Aperture vertically-round-oval, higher than wide ; outer lip 

 thickened and erect ; inner lip reflected, to a greater or less 

 extent, over the nearly straight pillar to form a flattened 

 callosity. The surface is ornamented with the finest pos- 

 sible sharp, thread-like, close, uninterrupted, oblique striae, 

 with longitudinal, or transverse bands of colour. 



Obs. — The channelling of the suture is seen in a more pro- 

 nounced form only in the larger specimens, but in some 

 of the latter it is particularly well marked (PL III., Fig. 1), in 

 others it is not more than ordinarily so. The spire varies in 

 height to some extent ; in certain individuals it is depressed, 

 giving to the shell quite a neritina-\^Q aspect, in others it is 

 more elevated and distinct. This is more particularly the 

 case with those specimens obtained from the " Buckie-fake," 

 although both forms are present amongst the examples from 

 Fifeshire. The thread-like lines of growth which cross the 

 whirls obliquely, are, as a rule, very finely preserved (PL III., 

 Fig. 9), but occasionally they are only to be seen on the 

 shoulder of each whirl just below the suture ; this is a very 

 characteristic feature of the genus Naticopsis. The callosity is 

 of variable extent and development. In some examples the 

 reflection of the inner lip hardly amounts to this character, 

 being merely a thickening (PL III., Fig. 7) ; in others, on the 

 contrary, there is a decided spreading outwards (PL III., Fig. 

 7a). In a few of those with the callosity little developed, and 



