﻿66 BKITISII FOSSIL TRIGONI/E. 



Upper Lias : T. vavis, Tjiim., T. puIcJiclln, Ag., T. tuberciihtta, Ag. {T. spirmJom, Y. and 

 B.), T. shiiills, Bi'onii, and T. costellata, Ag. Subseciuent researches have shown that 

 the latter five species are associated more or less one Avith another in a single geological 

 position, and that two or more of them occur together at several localities in Southern 

 Germany. Professor Quenstedt (' Der Jura.') has established T. /i«ywaiid T. pulchella as 

 species of the lower portion of the Lifcrior Oolite. 



\n Britain T. spiiiiilosa pertains both to the Supra-Liassic Sands and to the lower 

 portion of the Inferior Oolite ; and, as the two remaining species arc associated in Southern 

 Germany with the three former, it may be inferred that all of them belong to a higher 

 position than T. literata, and that the latter therefore occupies the lowest position of any 

 known species of the Upper Lias. 



In Britain T. lileraia has occurred only at a single locality ; namely, a little higher than 

 the middle of the llpper Lias Shale at the Peak, Robin Hood's Bay, in scars accessible only 

 at low water ; there are no Ammonites in this stratum, but it inunediately overlies a bed 

 with Ammonites crassiis, Y. and B. ; it is lower than the beds worked for alum upon the 

 same coast. Specimens occur of every stage of growth, with the valves both united and- 

 separated; but, as the greater number have the characters of the surface ill-preserved, good 

 specimens arc somewhat rare. 



Trigonia V-costata, Lijc. Plate XIH, fig. 5 ; Plate XV, figs. 1, 2, 3, 4. 



Trigonia angclata, Phil. Geol. York., 1829, vol. i, p. 15G (not Sow.). 



— — Williamson. Ou Distribution of Fossils, Yorkshire Coast, Trans. 



Geol. Soc., 1836, 2 ser., iii, p. 229. 



— v-cosTATA, Lycett. Ann. and Mag. Nat. Hist., 18J0, p. 422. 



— — Morris. Catalogue, IS;")!, p. 228. 



— — Lycett. Cotteswold Hills Handbook, 1857, pi. vi, fig. ."J. 



Shell ovatcly trigonial, moderately convex ; und)ones nearly mesial, produced, obtuse, 

 and usually somewhat recurved ; anterior side produced, its border curved elliptically 

 with the lower border; hinge-border slightly concave, sloping obliquely, its extremity 

 forming an obtuse angle with the extremity of the area. Area narrow, concave beneath 

 the apices, but flattened posteally ; it is traversed transversely by delicate plications, 

 which near to the apices form a few regular, smooth costella> ; it has a mesial longitudinal 

 furrow, and in the young condition three closely tuberculated carin;c, which become 

 evanescent posteally with advance of growth. The escutcheon is much depressed compared 

 with the inner carina ; it is lengthened, of moderate breadth, and pcrllectly flat. The 

 other portion of the surface has the rows of costae numerous (twenty to twenty-four) and 

 narrow ; they are but little raised, and are rather inconstant in their characters ; sometimes 



