PLATE LXXY. 
1. Trigonia Angulata. (Angular Trigonia.) Transversely sub-triangular, elongated; convex; anterior side sub- 
arcuated ; surface, with transverse, curved ribs, changing into series of nodules ; posterior side produced, divided from 
anterior by curved, crenated rib; crossed by transverse striae ; upper edge concave. 
2, 3. T. Imbrieata. ( Imbricated Trigonia .) Triangular, compressed; anterior side, with five or six, transverse, 
imbricated ribs; posterior side obliquely truncated, with transverse, flattened ribs. 
4. T. Costata. ( Ribbed Trigonia .) Trigonal; posterior side ventricose, with transverse, smooth ribs ; anterior side 
large, divided from flattened anterior by elevated, crenated rib from beak to margin; intercostal spaces, with several, 
longitudinal, crenated strife; beaks central, sub-acute. 
5. T. Quadrata. ( Squarish Trigonia .) Sub-quadrangular, compressed ; anterior side short, rounded ; posterior side 
broad, truncated; beaks obtuse; upper line straight; basal line arcuated; surface, with concentric ribs, bent at centre, 
where is a line of large tubercles. 
6. Trigonellites Latus. ( Broad Trigonellites.) Sub-triangular ; anterior side, concave below beaks ; posterior straight, 
with longitudinal sulcus from beaks to side; basal line arcuated; surface smooth, with concentric lines of growth ; beaks 
.acute; porous inside. 
7. T. Alseformis. (Wing-shaped Trigonia.) Sub-triangular, wing-shaped; anterior side arcuated, with many trans¬ 
verse, tuberculous ribs ; posterior side lengthened into acuminated, sub-truncated beak, with broad, curved ridge; beyond 
the ridge a flat space, crossed by flat, oblique ribs ; beaks acute, incurved. 
8. T. Spinosa. ( Spinous Trigonia.) Obliquely ovate, compressed; beaks obtuse; anterior side large, separated from 
posterior by oblique ridge from beaks to margin, with many, spinous ribs on each side, producing crenulated margin. 
9. T. Spectabilis. (Notable Trigonia.) Sub-ovate, sub-trigonal, convex; with obtuse, central elevation from beaks 
to base; beaks obtuse; near them three or four, smooth, concentric ribs; surface smooth, with seven or eight, semi-circular 
rows of large, blunt tubercles ; edges straight, undulous; base rounded. 
10. T. Nodosa. ( Nodulous Trigonia.) Obovate; beaks obtuse, central; surface smooth, with indistinct rows of large 
knobs; anterior side rounded; posterior side straight from beak for two-thirds of length of valve; anterior side arcuated ; 
base rounded. 
11. T. Clavellata. (Club-shaped Trigonia.) Sub-triangular, elongated, curved; anterior side straight, with three, 
longitudinal rows of small tubercles ; posterior side arcuated, with from twelve to fourteen series of rounded tubercles; 
surface roughish ; beaks small, curved. 
12. T. Pustulata. (Pustulous Trigonia.) Sub-triangular, gibbose ; anterior side rounded; posterior side sub-trun¬ 
cated; back concave, base arcuated; beaks obtuse, incurved; surface, with concentric sulci; anterior portion with series 
of oval pustules. 
13. T. Gibbosa. (Gibbous Trigonia.) Sub-triangular, obliquely elongated, gibbose ; anterior side straight; posterior 
side produced, sub-truncated, with longitudinal sulcus ; beaks narrow, incurved, close ; basal line arcuated; back concave ; 
surface smooth, with transverse lines of growth. 
14. 15. T. Cuspidata. (Pointed Trigonia.) Sub-triangular, compressed; anterior side rounded; posterior side trun¬ 
cated ; surface, with about seven, concentric ribs; beaks acute; back rounded; basal line arcuated; shell thin. 
16,17. T. Pullus. (Bug Trigonia.) Sub-triangular, inflated ; anterior side rounded ; posterior side truncated; beaks 
obtuse; anterior portion, with many, transverse ribs, separated from other side by longitudinal, crenated rib ; lunette 
large, striated. 
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