52 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 
testacea, which are believed to represent estuary conditions, a geological horizon which 
possibly is not very dissimilar to that of our specimen. 
Triconia aRata, Lyc. Tab. XL, fig. 2. 
Testa ovato-trigona, subdepressa, umbonibus antemedianis, obtusis depressis, latere 
antico brevi, rotundo, postico oblique declivi, area planata, oblique irregulariter, striatis, 
carina marginali subnullo, lateribus costis antice obliquis, posticé angulatis, depressis, sim- 
plicibus. Testa etate juniori costis concentricis simplicibus. 
Shell ovately trigonal, somewhat depressed; umbones anterior to the middle of the 
valves, obtuse and depressed ; anterior side short, rounded ; posterior side sloping obliquely 
down ; area flattened, with transverse, irregular striations ; marginal carinz not conspicuous, 
and obsolete posteriorly ; the sides of the valves with numerous closely arranged, oblique, 
plain coste, which are bent upwards posteriorly at an obtuse angle, and meet the area at 
a right angle. 
The costee are rounded and rather depressed; they become more distantly arranged 
posteriorly, but only slightly increase in size. The young shell has the coste regular 
and concentric; the marginal carina is small, but forms a distinct elevation ; a specimen 
more aged than the one selected for our figure has the posterior portions of the coste 
slightly nodulous ; anteriorly they become waved and irregular. 
Geological Positions and Localities. A yare species; Mr. Walton’s specimens are 
from the Forest Marble of Farleigh, near Bath ; it has also occurred in the same position 
near to Cirencester. 
Triconia Batuontca, Lyc. Tab. XU, fig. 3. 
Testa subtrigona, depressa, umbonibus altis mediantis, latere antico et postico subrecto, 
oblique declivi, lateribus costis elevatis, angustis, crebris, subundulatis, et spinulosis, 
oblique instructis ; area parva planata oblique striata, carina marginal minimo, subnullo. 
Shell subtrigonal, short, depressed ; umbones elevated, mesial, and not recurved ; anterior 
and posterior borders nearly straight, sloping obliquely downwards, the surface with 
numerous (about twenty-four) narrow, elevated, spinose, and somewhat undulated oblique 
costee, which are directed from the marginal carina anteally downwards, and all reach the 
lower margin ; the area is narrow and obliquely striated ; the marginal carina is very small, 
and rather indistinct. 
The narrow, ridge-like costa have numerous minute, obtuse spines, which impart 
roughness to the surface; they are distinct, rather irregular, and therefore very different 
from the serrated, elevated, regular coste of 7. striata, Miller, and its allied species; the 
