296 J. Starkie Gardner — On the Gault Aporrha'idce. 



The fourth, which is the first descending the spire, is seen to be 

 slightly ribbed; as the whorls increase in size, the ribs, which are 

 narrow and slightly flexuous, become more pronounced, reaching 

 their maximum prominence on the penultimate whorl, where they 

 are 17 or 18 in number ; this number is, however, variable, and the 

 ribs are often irregularly distributed ; on the last whorl they be- 

 come shortened and tubercular as they approach the outer lip, and 

 form a ridge on the wing ; this whorl is slightly angular or carinated, 

 and generally carries an indication of a second anterior keel. All 

 the whorls are faintly striated spirally, except near the suture, where 

 two or three striae are strongly marked. The outer lip, in adults, 

 is produced into an expanded wing, prolonged posteriorly into an 

 oblique point ; the outer margin is nearly straight, and anteriorly 

 there is a slight sinus. The wing is attached to the penultimate 

 whorl. The aperture is narrow and the canal elongated. 



History. — This shell is generally known as B. Robinaldina of 

 D'Orbigny, described (1843) in the Pal. Fr. Terr. Cret. vol. ii. p. 282, 

 pi. 206, f. 4 and 5. Pictet and Campiche separate the British species 

 from that of D'Orbigny, which has, according to their views, a 

 shorter and thicker spire, whose length does not equal half that of 

 the whole shell, a less number of ribs, and these shorter on the last 

 whorl. They appear in doubt, however, as they add, " ce groupe est 

 difficile et renferme encore plusieurs especes inedites ou mal connues." 

 Not having hitherto had an opportunity of comparing actual speci- 

 mens, I am not in a position to decide the question, and reserve 

 comment for a future occasion ; but it is not unlikely, if the forms 

 are really distinct, that they both occur in England, some casts in 

 the Geol. Soc. Museum, from Shanklin and Pulborongh, possessing all 

 the characters indicated by Pictet aifd Campiche. A. acuta, P. and C, 

 and B. Alpina, are closely allied forms. A. simplex, D'Orb., belongs 

 to the Chalk Marl and Gault. Among English authors, J. Sowerby 

 first described it as A. Parhinsoni ; Forbes, in 1845, vol. i. Quart. 

 Journ., recognized its similarity with B. Bobinaldina, D'Orb. ; Fitton 

 in the Quart. Journ. vol. iii. gives it an extended range, Lower 

 Perna Beds to top of Cracker Group, bed No. 9 ; and Mantell, in the 

 Geology of the Isle of Wight, 1847, figured this shell under the 

 last adopted name. It has frequently been included in lists of 

 fossils since, and Mr. E. Tate described it in the paper several times 

 previously referred to. 



Distribution. — Abundant in the Lower Greensand of Atherfield, 

 Peasemarsh, etc. Pictet and Campiche name it as occurring in the 

 Lower Aptien of Ste. -Croix, Perte-du-Ehone, and Vassy. They have 

 named it A. Forbesii. 



Apokrhais glabka, Forbes. 



The following description is partly taken from Forbes's paper in 

 the Quart. Journ. of the Geol. Soc. for 1845, p. 350, pi. iv. f. 5. 



Whorls of spire convex and finely striated spirally, the striaa near 

 the suture being so deep as to give them a marginated aspect, and 

 crossed by oblong slender ribs, which are not very numerous. The 



