Vol. 58.] | JURASSIC OF THE SOUTH WALES DIRECT LINE. 721 
Paleontological Note. 
The Pectens, so common in the shales, exhibit several characters 
in common. They are all orbicular in form, have the front wing 
double the size of the hind one, and appear almost smooth to the 
naked eye. With a lens, however, fine radial and concentric striz 
are rendered visible; this ornament is quite clear to the unaided 
eye in P, textilis, Reem., is distinct with a lens in P. calvus, Goldf., 
while in P. subulatus, Munst., the radials are very indistinct. 
P. multifurcatus, Tate, has closely-punctated radials, which curve 
outward as they diverge (much after the fashion of P. rigidus, 
Sow.). 
(d) The Angulatus- Beds. 
The uppermost 17 feet of our first vertical section is characterized 
by a thick series of clayey shales, having three nodular limestone- 
beds at the base and capped, at the top of the section, by several 
bands of nodular limestone separated by thin clay-partings. The 
whole series is very fossiliferous, and its geological horizon is well- 
marked by Schlotheimia angulata and its mutations. Of these 
mutations the flattened and close-ribbed form characterizes the 
middle shales ; while the thicker form, with more widely-spaced and 
taller ribs, occurs in the uppermost nodular limestone-bands, where 
it is associated with Ammonites (Vermiceras) Conybeart. 
It is worth noting that the association of a species of Schlotheimia 
with Amm. Conybeari at the top of the Angulatus-zone is common 
throughout the Bristol district (as, for example, at Keynsham, where 
Schlotheamia Charmassei and Amm. Conybeart occur together). 
Rhynchonella calcicosta was found in the uppermost beds, but is 
of rare occurrence. In this association we see another point of 
resemblance with the same horizon near Bristol; but, whereas in 
the Sodbury district RA. calcicosta is very uncommon, near Bristol 
it occurs in thousands. 
The most abundant of all the fossils in this series of beds is an 
oyster (Ostrea wrregularis, Minst.) which exhibits a most puzzling 
variation of form. The unattached valve is always flat, with the 
beak slightly curved, the attached valve always deep and convex, but 
the area of attachment differs greatly in size and position in different 
individuals. When this area is large and flat the species resembles 
O. ungula, but there is a complete transition from such forms to that 
of a typical Gryphea, with incurved beak and deep, regularly convex, 
lower valve. No typical specimen of Gryphea arcuata was found 
in the beds, but the oyster now under discussion undoubtedly occurs 
on the same horizon as that at which Gr. arcuata is so abundant in 
the Bristol district ; moreover, an oyster of identical form is found 
associated with Gr. arcuata at several localities near Bristol. We 
are inclined to regard this oyster as a mutation of a species of 
Gryphea, but not identical with Gir. arcuata. 
Q.J.G.S. No. 232. 3D 
