J. Starkie Gardner — Cretaceous Gasteropoda. 107 



nearly round, and the lips not thickened ; but a specimen with the 

 aperture satisfactorily preserved is still a desideratum. 



In its young state the shell presents a somewhat different aspect, 

 and the first eight whorls, which may be considered apical, have but 

 seven or eight ribs, which are very salient and sharply defined, and 

 with smooth intervals ; at least, the striae can only be detected with 

 the aid of a microscope (Plate IV. Fg. 6). The striae appear on the 

 anterior part of the eighth and extend over the whole of the succeed- 

 ing whorls. The cast preserves the form of the ribs, but is other- 

 wise smooth ; the whorls appear very inflated and separated by very 

 deep sutures. 



This shell was first described and figured by d'Orbigny, 1842, in 

 the Pal. Fr. Terr. Cret., vol. ii. p. 154, and again by Pict. & Koux, 

 1849. The original of d'Orbigny's figure is now in the Ecole des 

 Mines ; the mouth is very imperfect, and has evidently been restored 

 in the drawing. It occurs constantly in lists of Gault fossils, and 

 appears to have a wide range in France and Switzerland. 



In England it is characteristic of the Gault and Upper Green- 

 sand, it being abundant both at Lyme Kegis and Folkestone. 

 Specimens are in the British Museum from Devizes, and a fine ex- 

 ample of the young state of this shell, from Blackdown, is figured 

 (Plate III. Fig, 15), whence, however, no full grown specimens have 

 been obtained. No species of true Scalaria has hitherto been found 

 in the Cambridgeshire district. Most of the Lower Greensand local- 

 ities cited probably refer to other species. These are described 

 further on. ScalaShutanurensis, Stoliczka, of the Pal. Indica, is prob- 

 ably this species, the only difference noticed being a supposed 

 coarser striation. Sc. ornata, a Cretaceous form from South Africa, 

 also cannot be distinguished from this. 



This and the various allied species are eminently characteristic of 

 the Cretaceous age, and would alone serve to determine rocks of this 

 age in any part of Europe. 



Sc. CANALiGULATA. d'Orb. Ncocomian. Plate III. Figs. 5, 6. 



Shell elongated, angle 16°; whorls numerous, rounded and in- 

 flated ; ribs seventeen, well defined and regular, salient and rounded, 

 nearly parallel with the axis ; strise very fine and even, seen, 

 when strongly magnified, to be crossed by fainter transverse lines 

 (Plate III. Fig. 5a) ; sutures distinct and slightly keeled ; the last 

 whorl with the usual roll-like collar^ round the umbilical region, 

 which is more distinctly and deeply striated, and is also marked by 

 lines of growth. What has the appearance of being the mouth is 

 ovate and the lips thin. Tho cast is smooth, but with traces of the 

 ribs preserved. 



A second specimen has the whorls slightly more depressed than is 

 represented in Fig. 5, has rather stronger ribs, fourteen in number, 

 and is without striae. 



^ I use the term collar for the keel on the basal whorl, against which the ribs 

 terminate. 



