TERTIARIES OF THE EAST OF ENGLAND. 121
Chillesford Beds.
Abra prismatica is given in the list in the Supplement to the 1 Crag Mollusca' as doubtful from these beds. An undoubted specimen has been sent me from Aldeby, by Mr. Dowson ; and he informs me that he has obtained several there.
In addition to the species given in the Synoptical List in the Supplement to the ' Crag Mollusca.' I have since identified the fol- lowing from specimens obtained by Mr. Harmcr and my son.
Lower Glacial Sands.
Buccinuni undatum, Linn., var. tenerum, from Belaugb.
Melampus pyramidalis, J. Soivcrby, from Rackheath.
Cardium islandicum, Linn., from Belaugb. A doubtful identification.
Honax vittatus, La Costa. One specimen from Belaugb, and two from Wey-
bourne. Thracia papyracea, Poli, from Belaugb. One perfect specimen. Cyrena fluminalis, Midler, from Belaugb. Small.
Middle Glacicd.
Hydrobia ulvse, Pennant, from Lound, near Yarmouth. One perfect specimen.
Mactra arcuata (?), J. Sow. Part of tbe binge of a specimen of Mactra occurred in tbe shell-band in tbe well two furlongs north of Seckford Hall, Great Bealings, wbicb shows the ridged or striated markings on tbe lateral teeth. No other species known to me of that branch of the genus which bas these markings woidd agree with tbe proportions of this fragment ; so that I bare little doubt, small as tbe fragment is, of its specific identity with M. arcuata. In tbe list accompanying Mr. Prestwicbs paper on tbe Crag, Mactra arcuata is assigned by Mr. Jeffreys as a variety of Mactra glauca (Quart. Journ. Geol. Soc. vol. xxvii. p. 484); but this shell belongs to the section of tbe genus which i3 destitute of tbe striated markings, and was made the type of the genus Mactra by tbe late Dr. Gray, while those species which possessed these markings were placed by him in a new genus, which be called Spisula, and of which he considered S. {Mactra) solida the type. The fragment in question, however, does not agree in its proportions with M. solida, but with M. arcuata, which, for the reasons just given, I still consider different from any species yet known as living. Other portions of the shell also occurred with it.
Postglacial.
Trochus helicinus, Fabr. A perfect specimen from March. This species rarely inhabits the Shetland Seas, but is common in all Arctic seas, and is fossil in the Clyde beds.
Tapes, either pullastra, W. Wood, or virgiueus, Linn. A fragment from Hun- stanton.
Tellina lata, Gmcl. A specimen from the March gravel in the Cambridge Museum.
Cyrena fluminalis, MyZler. Numerous specimens from March.
{For the Discussion on this paper see p. 140.)
