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SUPPLEMENT TO THE CRAG MOLLUSCA. 



Unio pictorum, Linne. Supplement, Tab. VIII, fig. 3. 

 Locality. Post Glacial, Grays. 



In the 'Crag. Moll./ vol. ii, p. 99, Tab. XI, fig. 13, is the representation of a shell 

 from Stutton, which is there called M. tumidus, but the specimen was not in very perfect 

 condition, and its correct reference is by no means certain. The specific line of separa- 

 tion between tumidus and pictorum is not easily determinable even in the recent state, and 

 less so with fossils. The specimen here figured was found by Mr. Pickering at Grays, 

 and to which he has given the above name. 



Unio tumidus, PMlippsson. Supplement, Tab. VIII, figs. 2 a, h. 

 Locality. Post Glacial, Grays. 



This is one of a group which is exceedingly abundant ; indeed, it was the only 

 form I could find at that locality after many days' search. It is a peculiar variety, being 

 more inequilateral than any recent specimens of that name which I have seen, the pedal 

 side being peculiarly short. The specimens at Grays lie there in myriads, but I have 

 never seen one approaching the dimensions of the recent shell, which is said to have reached 

 four and a half inches in length. The Grays specimens never exceed three inches, and 

 rarely attain to that size. In deference to those authors who have distinguished tumidus 

 from pictorum I have kept the two forms as distinct species, but in my opinion the two 

 graduate into each other, and are not distinguishable. 



In 1864 I found an imperfect specimen of Unio in the Eluvio-marine Crag at Bra- 

 merton, but unfortunately this was not perfect enough for representation or determination. 

 It appeared to resemble M. tumidus, and I have provisionally referred it to that species. 

 This same inequilateral form tumidus also occurs at the base of the bed E of Sect. V 

 (Kessingland) of the map sheet accompanying the introduction to this Supplement. 



Unio littoralis, Lam. Crag Moll., vol. ii, p. 98, Tab. XI, fig. 12. 



I have hunted at Grays for several years without finding this species, and Mr. 

 Pickering tells me he has not been able to find it there, but Sir Charles Lyell has shown 

 me some specimens which he obtained at that locality many years ago, that undoubtedly 

 belong to this species. 



