112 SUPPLEMENT TO THE CRAG MOLLUSCA. 
Belaugh, and Weybourn. Middle Glacial, Billockby, Clippesby, and Hopton. Upper 
Glacial, Dimlington, and Bridlington. 
This shell has recently been identified with JV. Zyalli from ie north-west coast of 
America, and by others with JV. zasegnis from Japan, while there is a third shell that has 
equal pretensions to identity, viz. JV. mirabilis (Adams and Reeve) ; all these having the 
exterior ornamentation like that upon the upper part of WV. Cobéoldie, but none of these 
living shells, so far as they are known, approach in size any of the fossil specimens, 
those of 4. Lyalli that I have seen being not more than half in linear dimension ; and, 
as pointed out by me originally (‘ Crag Moll.,’ vol. 1, p. 83), two Cretaceous species are 
similarly ornamented. All the specimens of these Pacific shells, which I have yet seen, 
are destitute of that broad exterior belt extending from a fourth to a third of the shell’s 
diameter, which is free from the oblique or zig-zag markings, and forms the margin of 
the full-grown specimens of JV. Cobdoldie from the Red Crag at Butley, and from the 
successive Glacial beds of Hast Anglia. In order to show this belt I have had a specimen 
figured from Belaugh. 
If the recent shells which I have seen and which are all destitute of this plain belt 
should prove to be only young individuals, which, when full grown, would acquire it, 
LV. Cobboldie would, nevertheless, not agree with them, because the tumidity and more 
elevated umbo of all these Pacific shells is such, that if they grew to the size necessary to 
add on the belt they would assume a very different form than that of Cobboldie; and 
these recent shells are also more angular than our fossil. I, therefore, still retain this well- 
known fossil as a distinct species. 
No trace of this shell has yet occurred in that part of the Red Crag which exists at 
Walton Naze and which I regard as the oldest part of that formation, and as possessing 
Mediterranean affinities, but it gets more common in the newer portions of the Red Crag 
with northern affinities. In the Butley Red Crag Cobdoldie@ is common, as it is also at 
some localities of the Fluvio-marine Crag and of the Chillesford bed. In the Lower 
Glacial sands it is rare where these sands are Fluvio-marine, as at Belaugh, but 
commoner where they are more marine, as at Weybourne. It is very abundant, in a 
fragmentary condition, in the Middle Glacial sands, and it appears to be characteristically 
the sheli of the Pre-glacial and earlier Glacial periods, and to have disappeared from 
British seas towards the later part of the Glacial period.’ 
The shell called Nucula (Acila) Lyalli, by Mr. Bell (‘ Ann. and Mag. Nat. Hist.,’ 
1871), was placed in my hands, and I believe it to be only the young state of Cobboldie. 
1 In the foot-note to p. 26 of the Introduction to this Supplement, mention is made of a thin band of 
sand intercalated in the upper glacial clay at Dimlington, which contained mollusca with valves united. 
Since that note was published some specimens from this bed were kindly forwarded by Sir Charles Lyell, 
and among these were several of Nucula Cobboldie. Mr. Leonard Lyell’s description, which Sir Charles 
forwarded with the specimen, speaks of this sandband having been literally packed with perfect specimens 
of Nucula Cobboldie. 
