116 SUPPLEMENT TO THE CRAG MOLLUSCA. 
Arca TETRAGONA, Pol. Crag Moll., vol. u, p. 76, Tab. X, fig. 1. 
Localities, Cor. Crag, Sutton, Ramsholt, and Sudbourn. Red Crag, Sutton. 
The specimen represented in figs. 1 @ and 6 (‘Crag Moll.’) is from the Red Crag at 
Sutton, and, it was there considered as belonging to the above-named species ; figs. 1 ¢ and 
1d are from the Coralline Crag. In the ‘Brit. Conch.,’ vol. u, p. 181, 4. tetragona is 
stated to be in the Red and Cor. Crag, but in the list accompanying Mr. Prestwich’s paper 
this species (¢e¢ragona) is given from the Cor. Crag only, while my shell from the Red Crag 
is referred by this author to 4. zmbricata, Poli. In consequence of this statement I have 
again examined and compared my specimens with the Mediterranean shell, but must still 
retain my previously formed opinion. 
PECTUNCULUS GLyCcimERIS, Zinn. Crag Moll., vol. u, p. 66, Tab. IX, fig. 1. 
Localities. Cor. Crag passim. Red Crag passim. Fluvio-marine Crag, Bramerton. 
Chillesford bed, Aldeby: Middle Glacial, Billockby and Hopton. Upper Glacial, 
Bridlington. 
The genus Pecfunculus is one in which the species are of very difficult determination, 
as may be seen by the number of synonyms given by various authors, and the little 
accordance there is as to specific separation. In the Cor. Crag the prevailing form is the 
thick variety, corresponding in this respect with the Mediterranean shell or rather with the 
Sicilian fossils, but I have also found in the Cor. Crag the thinner and less tumid shell, 
hike that of the recent British variety. In the ‘Crag Moll.’ I gave P. glycimeris and 
P. pilosus as varieties of one species, following the authors of the ‘ Brit. Moll.,’ and I see 
no sufficient reason to alter that opinion. All J can say is that, if there be two species, 
as appear to be made out of these two varieties by some authors, they are both present in 
the Coralline Crag as well as in the Red. Mr. Canham has obtained from the Red Crag 
at Waldringfield a specimen which measured 3? of an inch in one direction and 
34 in the other, and this of great solidity, and with these are specimens thin and oblique, 
while some have prominent umbones; in others this part is much depressed, with every 
intermediate shade of difference. Itis difficult to say whether the thick shells in the Red 
Crag are, like the thinner ones, natives of the Red Crag sea, or whether they be derived 
from the Cor. Crag, as I think there can be no doubt that a large proportion of the 
Pectunculi, which make up the mass of the thin bed at the base of the Red Crag, from 
which the phosphatic nodules are extracted, have been thus derived. P. sted/atus and P. 
ensubricus are, I believe, mere varieties of this species. P. glycimerzs (I presume the thin 
