Tiir 



CONCHIFERA. 



1S3 



tuso ; superior line nearly straight ; basal line a little arcu- 

 ated ; surface with concentric ribs, each of which is bent at a 

 right angle in the raiJillo, where there is a line of large tu- 

 bercles extending in an angle from the beaks to the margin. 

 The Greensand, Blackdown. 



10. TiiiGO.NiA spi.vosA. — The Spinous Trigonia, pi. LXXV. 

 fig. 8. 



T. npinota. Parkinson, Org, Rem. II. pi. 12, fig. 7. 

 Sowerby, I. p. l.'>6, pi. 86. Var. lb. Goo. Trans. 2d Ser. IV. 

 p. 190, pi. 13, fig. 3. 



Obliquely ovate ; compressed ; beaks obtuse ; anterior side 

 large, and separated from the posterior by an oblique ridge 

 extending from the beaks to the margin ; on each side of 

 which the surface is covered with many divergent spinous ribs, 

 beniling upwards, and increasing in thickness as they diverge 

 from the ridge, and producing a crenulated margin all round. 



The Lower Greensand, Seabrook, Pulborough, Sandgate, 

 and Lyme Regis. 



11. Trigonia spectabilis. — The Notable Trigonia, pi. 

 LXXV. fig. 9. 



T. upectaliUs. Sowerby, AT. p. 83, pi. .54*. 



Sub-ovate, sub-trigonal, convex ; an obtuse, nearly central, 

 slightly curved elevation, emanates from the beaks, and ter- 

 minates on the base ; beaks obtuse, a little turned to one side ; 

 near to them, three or four smooth, concentric, rounded ribs ; 

 surface almost smooth, with seven or eight semicircular rows 

 of large, blunt, round tubercles, and a few irregular smaller 

 ones on the posterior side ; both edges rather straight, undu- 

 lous, produced by the projecting tubercles ; base rounded. 



The Greensand, Blackdown. 



12. Trigonia nodosa. — The Nodulous Trigonia, pi. 

 LXXV. fig. 10. 



T. nodosa. Sowerby, V. p. 7, pi. 507, fig. 1. 



Somewhat obovate ; beaks obtuse, and nearly central ; sur- 

 face smooth, covered anteriorly with indistinct, irregular rows 

 of large, depressed knobs, and some smaller ones on the poste- 

 rior portion ; anterior side rounded, or arcuated ; posterior 

 side nearly straight from the beak for two-thirds the length of 

 the valve ; anterior side arcuated ; base rounded. 



The l/ower Greensand, Seabrook, Kent. 



13. Trigonia clevellata. — The Club-shaped Trigonia, 

 pi. LXXV. fig. II. 



T. cleeellala. Parkinson, Org. Rem. III. p. 175, pi. 12, 

 fig. 3. Sowerby, I. p. 197, pi. 87, upper figs. 



Sub-triangular, obliquely elongated, cur\'ed ; anterior side 

 straight, flattened, with three longitudinal, linear rows of small 

 round tubercles ; posterior side much arcuated, with from 

 twelve to fourteen transverse, curved series of rounded 

 tubercles ; the surface rather rough ; anterior seam undulous, 

 slightly caping under the curved and small beaks. 



The Lower Greensand, Seabrook, Kent ; the Portland 

 Stone, Langconibo and Swindon ; and the Kelloways Rock, 

 Weymouth and South Cave. 



1*. Trigonia oibbosa. — The Gibbous Trigonia, pi. LXXV. 

 fig. 13. 



T. gibhosa. Sowerby, III. p. CI, pi. 235. 



Sub-triangular, transversely elongated, obli(|iio, and gibbose ; 

 anterior side nearly straight ; posterior side produced, nar- 

 rowed, and obliquely sub- truncated, with a broad, oblique. 



longitudinal, shallow furrow, or depressions emanating from 

 the beak, and terminating on the extreme point of the some- 

 what beaked terminations ; beaks narrow, incurved, and 

 approximating ; basal line regularly arcuated ; back concave ; 

 surface smooth, with tran.sverse, shallow lines of growth, 

 which increase in depth ami jiroxiraity at the base. 

 The Lower Greensand, Lockswell Heath. 



15. Trigonia pustulata. — The Pustulous Trigonia, pi. 

 LXXV. fig. 12. 



T. gibhosa. Var. B., Sowerby, III. p. 61, pi. 230. 



Sub-triangular, gibbose ; anterior side rounded ; posterior 

 side produced, and obliquely sub -truncated ; bax;k somewhat 

 concave ; base considerably arcuated anteriorly, and poste- 

 riorly a little concave, giving it a beaked aspect ; beaks ob- 

 tuse and incurved ; whole surface with shallow concentric 

 furrows, the anterior portion with series of irregularly set, 

 oval pustules. 



The Portland Stone, Portland ; the Vale of AVardour ; 

 Swindon, and Brill. 



AIthouf;h the two preceding shells bear a striking similitude in form, 

 yet I cannot agree with Sowerby and others that they are the same 

 species. 



16. Trigonia cuspidata. — The Pointed Trigonia, pi. 

 LXXV. figs. U, 15. 



T. cuspidata. Sowerby, A^I. p. 8, pi. 507, figs. 4, 5. 



Sub-triangular, compressed ; anterior side rounded ; poste- 

 rior side abruptly truncated, with a projecting tag at its lower 

 angle ; surface with about seven concentric ribs, which are 

 pointed and angular at the posterior division of the valves ; 

 beaks acute ; teeth of the hinge much elongated ; back 

 rounded; basal line arcuated ; texture of the shell thin. 



The Great Oolite, Anclifi", Wiltshire. 



17. Trigonia pcllfs. — The Bug Trigonia, pi. LXXV. 

 figs. 16, 17- 



T. pttUm. Sowerby, VI. p. 10, pi. 508, figs. 2, 3. 



Sub-triangular, iuflated ; anterior side rounded ; posterior 

 side obliquely truncated, angular at its lower extremity ; beaks 

 rather obtuse ; anterior portion with numerous transverse? 

 smooth ribs, and separated from the other side by a longitudi- 

 nal, rather thickened, curved, slightly crenated rib, with seve- 

 ral similar ones on the flattened posterior side ; lunette large 

 and transversely striated. 



The Oxford Oolite, Upware, near Cambridge, and the 

 Great Oolite, Anclift", and Cain's Cross. 



18. Trigonia affinis.— The Allied Trigonia, pi. LXXVI. 

 fig. 41. 



T. ajfinis. Sowerby, III. p. 11, pi. 208, fig. 3. 



Transversely ovate ; anterior side rounded, smooth, ami 

 covered with transverse, flattened ridges ; posterior side a little 

 produced, slightly and obliquely sub- truncated, a little beake<l 

 at its lower angle ; basal line nearly straight ; beaks very ob- 

 tuse. 



The Greensand, Blackdown an I Parliam. 



1.9. Trigonia eccentrica. — The Eccentric Trigonia, pi. 

 LXXVI. fig. 45. 



T. eccentrica. Parkinson, Org. Rem. III. p. 175, pi. 12, 

 fig. 5. Sowerby, III. p. 11, pi. 208, figs, 1, 2. 



Tr.ansverscly sub-triangular, convex ; anterior sido short, 

 rounded ; posterior sido elongated, acuminated, and truncated ; 

 its length little more than half its width ; beaks obtuse, in- 



