404 MOLLUSCA. TRIGONIADtE. Tuigonia. 



trigoniam:. 



Gen. TRIGONIA. — Equivalve, unequilateral trigonal; on 

 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. Rem. iii. 175, t. xii. f. 4 Sower. Min. Conch, t. lxxxv.— 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. Hem. iii. 177- t. xii. f. 7-— 

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



3. T. clavellata Triangular, rather wider than long, with ten or more oh- 



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. lxxxvii. — Oolitic Series. 



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

 anterior side angular, with many 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. Min. Conch, t. lxxxviii. 

 — Green Sand. 



5. T. eccentrka Transversely ovate, convex ; anterior side produced. 



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

 Org. Rem. iii. 175, t. xii. £ 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. aliformis.— "Wing-formed; anterior side produced, truncated, with a 

 broad compressed ridge extended to the beak ; posterior side costated, round- 

 ed ; costte 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. 

 Upper 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 — Soiver. Min. Conch, t. ccxxxvii. f. 1, 2, 

 3. — Inferior Oolite. 



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

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

 middle are longitudinal crenulated costae, suddenly reflected over the poste- 

 rior side ; on the front are short intermediate ridges.— So wer. Mm. Conch. 

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



