OOLITIC BIVALVES. 
93 
i’ib being- divided into two strong ridges, and some of these 
are again duplicated and occasionally interlined (figs. G, 7). 
The flatter valve (figs. 5, 5 b) has much more numerous 
ribs, generally three to an internal rib, and these are much 
more equal in thickness than in the other valve. All are 
crossed by lines and ridges of growth, and well preserved 
specimens show distinct but slender striae crossing the ribs in 
a regular manner, and decussating them. Fig. 7 b does not 
show this character so perfectly as would be desirable. 
This pretty species will agree with none in the British Col¬ 
lections; but Pec ten paradoxus , (Goldfuss, plate 99, fig. 4), 
from the Lias of Bavaria, is like it, and P. Massabnghi, figured 
in the Abbe StoppanFs work on the Lower Lias, or Kossen 
beds of Lake Como, has much the same character. Neither 
have the coarse external ridges. 
PECTEN MONILIFER.-V. Sp. 
Plate 22, fig. 10. 
A species not remotely allied to such species as P. articu- 
latus, Sehloth., and less closely to such as P. barbatus x Goldf. 
From the former, an inferior Oolite species, it is at once dis¬ 
tinguished by the few ribs, not above half the number occur¬ 
ring in the Himalayan form. Nor is the ornament quite 
like. 
We have three specimens, all imperfect. The shell was 
more than half an inch long, and about as broad, with a 
generally oval appearance. It is convex in the larger valve, 
and nearly flat in the other. Both valves have five or six 
large angular ribs, the interstices being angular likewise, and 
crossed by very fine, close lines of growth. The side ribs be¬ 
come duplicated, having smaller ribs of like character on their 
flanks (fig. 10 b). The lines of growth are stronger and 
more rugged in some specimens than others. The main ribs 
are strongly angular, and ornamented b} r equi-distant tubercles 
or short spines, so regularly placed as to suggest the name. 
