52 
THE LOWEK LIAS OF KEYNSHAM. 
Pholadomya : 
P. glabra, Ag. is abundant at Redland in tbe Ostrea beds 
and lower Psilonotiis zone. 
Other Pholadomyas occur in the Anyulafiis beds, but are 
usually badly preserved. 
Unicardium : 
U. cardioides, Phil, is common in the lower beds. 
Brachiopods. 
Spiriferina — 8. pinguis, Ziet is not uncommon ; no 
specimen of 8. walcotti has been found by us at Keynsham. 
Terebratiila — T. {Waldheimia) perforata, PiqUq. {T. sar- 
thacensis, d’Orb.) This is one of the most abundant fossils of 
the district ; it varies slightly in shape, yielding broader and 
narrower forms. The figure of T. psilonoti, Quenst. given 
in Der Jura (t. 4, f. 21), represents exactly the commonest 
form found near Keynsham. 
Rhynchonella : 
Rli. calcicosta, Quenst. 
This is by far the commonest fossil in the district and, 
though subject to great variation in the number of folds, is 
sufficiently" well marked out by the following characters : — 
Test small, both valves convex and usually meeting at a 
sharp angle, mesial sinus shallow, ribs sharp, tall and 
continuous to the beak, beak small and usually erect exposing 
the foramen. The normal mutation consists in the variation 
of the number of ribs ; an average Keynsham specimen has 
four ribs on the fold and four on each flank, but these 
numbers can be increased to six on the fold and seven on 
each flank, when the form agrees with Rh. plicatissima, 
Quenst. on the other hand, a reduction to three on the fold is 
of very common occurrence. Occasionally the surfaces of the 
two valves are continuous across the junction. 
