W. H. Eudleston—On the Yorkshire Oolites. 153 



Fig. 10, 10a. Another specimen. Same horizon, locality, and 

 collection. 



Length 22 millimetres. 



Width of last whorl to length of shell 56 : 100. 



Approximate spiral angle 41°. 



Portions of 6 whorls are visible. This is a very massive specimen : 

 the shell substance is extremely thick ; the body-whorl much in- 

 flated, the keels prominent and slightly lower than in Figure 9. 

 The spiral lines are proportionally coarse and salient. The body- 

 whorl carries a very large and prominent median keel, and this 

 supports a very stout digitation, which extends for m.ore than 10 

 millimetres at i-ight angles to the axis and then curves upwards. 

 The lower keel is observed distinctly to fade away and terminate at 

 the margin, beneath this great digitation. The base of the shell is 

 marked with spiral lines which decussate with an axial system of 

 lines producing an elegant mesh : this is especially the case below 

 the second or abortive keel. 



Notwithstanding differences, which are striking at first sight, 

 this specimen, it seems to me, is nothing more than a very robust 

 example of the wide-angled section of Al. bispinosa. Except in the 

 stoutness of the shell substance and the comparative coarseness of the 

 ornamentation, its elements are the same as those of Fig. 9. The 

 stoutness of the shell is probably the cause of so large a portion of 

 the wing-finger having been preserved. 



Relations and Distribution of the bis])inos a- group generally. — All 

 the indications seem to point to the fact that, as regards Yorkshire, 

 a group of shells having one long up-curved digitation, proceeding 

 from a body-whorl witli one principal carina, extended from the 

 Cornbrash (rare) through the Kelloway Rock into the Lower Cal- 

 careous Grit. The process containing the canal was long, but with 

 us its actual termination is unknown, owing to the imperfection of 

 the specimens. Within considerable limits as to width of angle, 

 there is much similarity in the character of the spire, which, in all 

 cases, is entirely devoid of longitudinal costee or tuberculations. 

 Specimens from the Lower Calcareous Grit seem to have the keel 

 placed rather more anteriorly than is the case with specimens from 

 the lower beds, and this is the principal difference that can be noted. 

 As regards there being only one lateral digitation springing from 

 the body-whorl, the following figures bear testimonj^, viz. Plate VI. 

 Figs. 7, 8, 10, to which may be added the figures of the Lower 

 Calcareous Grit fossils (Geol. Mag. 1880, PI. XVII. Figs. Qa and 6c), 

 my former supposition to the contrary notwithstanding. Hence, the 

 shell has two processes ; one being the lateral digitation, and the 

 other the canal sheath, or tail, so that Phillips's term bispinosa is also 

 structurally descriptive. 



Although there is no positive evidence of this form having been 

 observed in the Oxford Clay of Yorkshire, it may be seen in collec- 

 tions from that formation, as it occurs in the south of England, the 

 processes being usually longer than in the species with two lateral 

 digitations known as trifida. I doubt not that a fuller examination 



