8 
TRIGONIA imbricata. 
TAB. DVII. —Jigs. 2 and 3. 
Spec. Char. Transversely oblong, depressed ; with 
5 or 6 concentric, dentated, subimbricated keels 
upon the rounded anterior side ; posterior side 
obliquely truncated, ribbed. 
The carinae upon the surface of this little shell resem- 
ble terraces one above the other ; each is divided into 
4 or 5 angular lobes. 
Imperfect specimens of this Trigonia occur in the Rev. 
Mr. Cookson’s collection of AnclifFe fossils. 
Fig. 3 is enlarged. 
TRIGONIA cuspidata. 
TAB. DVII.— figs. 4 and 5. 
Spec. Char. Obovate, depressed, ribbed ; poste- 
rior side truncated, its lower angle pointed ; 
ribs concentric, with projecting angles where 
they pass unto the posterior side. 
A delicate, slender shell. It has, in place of the keel 
(which in several other species runs from the beak to the 
lower angle of the posterior edge), only produced angles 
of the ribs, the last of which forms a strong point at the 
lower extremity of the truncation. The hinge teeth are 
unusually long. 
From the AnclifFe Oolite, w ith the last. 
Fig. 5. a magnified representation. 
