192 SUPPLEMENT TO THE BRITISH 



twisted character of Rh. inconstans, but with not more than twenty strong ribs on each 

 valve, and this variation so nearly approaches, by its smaller dimensions and less gibbous 

 valves, to some of the Abbotsbury specimens as to be scarcely distinguishable. Eig. 4 is a 

 still larger specimen, with not more than twenty-five or six strong ribs, and with an unsyin- 

 metrical frontal margin ; while in fig. 6 w r e have a young flattened shell of the same type. 

 None of these, however, seem to have attained the size or globose shape of the typical and 

 adult Rh. inconstans. 



Although Rh. inconstans is a common species in the Kimmeridge Clay of several 

 British localities, it is exceedingly rare in that deposit in the Boulonnais, for Mr. E. 

 Rigaux assured me that he never obtained more than one example, and neither Messrs. 

 Bouchard, E. Pellat, nor myself, who have so often searched the cliff's extending on both 

 sides of the town of Boulogne, have ever picked up a single example, nor have any traces 

 of the species been brought to light during the Sub-Wealden boring at Netherfield, near 

 Battle, in Sussex, though so many hundred feet of Kimmeridge Clay were traversed. 

 One or two examples of a Rhynchonella were, it is true, obtained, but they w r ere not 

 referable to the species under description. 



By some inadvertence, at p. 88, line 3, of my Oolitic Monograph, it is stated that the 

 shell was found in the " Oxford Clay " of Wooton Basset ; the word "Kimmeridge " must 

 be substituted for that of " Oxford." Prof. Judd mentions that Rh. inconstans occurs in 

 the Kimmeridge Clay of Speeton Cliffs (' Journ. Geol. Soc.,' vol. xxiv, pp. 231 and 240). 



In the Supra-coralline red or rusty-coloured ferruginous rocks of Abbotsbury, near 

 Weymouth, in Dorsetshire, we meet with a very variable species, sometimes recalling, as 

 we have already stated, certain exceptional forms of Rh. inconstans (Sup., PI. XXVI, 

 fig. S),Rh. pinguis (fig. 7), and Rh. pectunculoides,YX., and even Rh. lacunosa, Schlotheim 

 (fig. 9). Mr. Hudleston, who sent me these three specimens for illustration, observes that, 

 " If the three forms were taken by themselves they might very well represent three distinct 

 species, but that they are connected together by innumerable intermediate forms, which 

 leaves no doubt as to their belonging to a single species." He further adds, " The 

 Abbotsbury beds are the remnants of deposits which have no absolute representatives on 

 the coast, but which are certainly very near in position to the Coralline or Kimmeridge. 

 In south Dorsetshire these formations pass into each other by gradations, as it were, 

 but there is on the coast a line of demarcation above the Coral-bed, where Rh. inconstans 

 appears suddenly. There is no great change in the lithology, and the Ammonites in 

 both series appear to be the same ; hence the lapse of time is not great between this 

 muddy and disjointed Coral-band and the bed with Rh. inconstans." 1 The Abbotsbury 

 shell is considered by Mr. Hudleston to be very close to Rh. inconstans, but it does not 

 appear to have attained the dimensions of that species, for none of the specimens I have 



1 The reader is referred to Messrs. Blake and Hudleston's admirable memoir "On the Coralliftn 

 Rocks of England," published in the xxxiii vol. of the ' Quart. Journ. of the Geol. Society of London,' 

 p. 260, &c, 1877. 



