404 MOLLUSCA. TRIGONIAD^. Trigonia. 



TRIGONIAD^.. 



Gen. TRIGONIA. — Equivalve, unequilateral trigonal ; oii 

 the right valve are two oblong, flat, diverging hinge teeth, 

 transversely grooved on each side ; on the left valve four 

 flat hinge teeth, transversely grooved on one side only, dis- 

 posed in pairs ; ligament external, marginal. 



1. T. costata — Triangular, with transverse, smooth ribs ; anterior side 

 marked with many small, and three large, prominent, longitudinal, crenula- 



ted ridges Curvirostra rugosa, Luid. Lith. 36, t. ix. f. 714 T. cost. Park. 



Org. Item. iii. 175, t. xii. f. 4. — Sower. Min. Conch, t. Ixxxv. — Inferior Oolite. 



2. T. spinosa Roundish, depressed, many ribbed ; anterior side trunca- 

 ted ; ribs oblique, diverging both ways from the ridge that separates the an- 

 terior side ; set with short spines. — Park. Org. Rem. iii. 177- t. xii. f. 7- — 

 Sower. Min. Conch, t. Ixxxvi. — In Green Sand. 



3. T. c/aue//ato.^Triangular, rather wider than long, with ten or more ob- 

 lique rows of tubercles ; anterior side straight, with three longitudinal knot- 

 ted ridges — Luid. Lith. 36, t. ix. f. 107- Park. Org. Rem. iii. 175. t. xii. 

 f. 3. Sower. Min. Conch, t. Ixxxvii. — Oolitic Series. 



4. T. dcedalea. — Obtusely rhomboidal, with many oblique rows of tubercles ; 

 anterior side angular, with manj'^ scattered tubercles, and one longitudinal 

 row bounded by a longitudinal ridge, on which is another row of large tu- 

 bercles Park, Org. Rem. iii. 176, t. xii. f. 6. Sower. ]Mm. Conch, t. Ixxxviii. 



— Green Sand. 



5. T. eccentrica. — Transversely ovate, convex; anterior side produced, 

 posterior side round, with oblique undulating ridges on the surface. — Park. 

 Org. Rem. iii. 175? t. xii. f. 5. — Sower. Min. Conch, t. ccviii. f. 1, 2 — In 

 Green Sand. 



G. T. affinis Transverse, oval, gibbose, half covered by transverse ridges. 



Sower. Min. Conch, t. ccviii. f. 3 — Green Sand. 



7. T. a/z/brTOJs.— "Wing-formed; anterior side produced, truncated, with a 

 broad compressed I'idge extended to the beak ; posterior side costated, round- 

 ed; costae many, thick, irregularly crenulated, oblique, recurved, and atte- 

 nuated towards' the ridge on the anterior side, where they terminate — Park. 

 Org. Rem. iii. 176, t. xii. f. 9. Sower. Min. Conch, t. ccxv — In Green Sand. 



8. T. gibbosa. — Transversely oblong, gibbose, slightly arched, concentrical- 

 ly undulated, or irregularly sulcated ; anterior side separated by a broad 

 longitudinal furrow or plane space. — Soiver. Min. Conch, t. ccxxxv. ccxxxvi. 

 Ujypcr Oolite. 



9. T. striata Obtusely triangular, convex ; with arched, oblique, crenu- 



lated costse upon the middle and posterior side ; anterior side nearly covered 

 by numerous, elevated, sharp ridges — Sower. Min. Conch, t. ccxxxvii. f. 1, 2, 

 3. — Inferior Oolite. 



10. T. dupUcata. — Transversely oblong ; anterior side marked with small 

 undulating ridges, and bounded by a strong tuberculated ridge ; over the 

 middle are longitudinal crenulated costa?, suddenly reflected over the poste- 

 rior side ; on the front are short intermediate ridges. — Sower. Min. Conch, 

 t. ccxxxvii. f. 4, 5.— Inferior Oolile. 



