CLAVELLATiE. 45 



rows are also distinctive. The escutcheon in T. spinulosa is larger, the three tuberculated 

 carinas upon the area also distinguishes that portion of the shell. 



Geological positions and localities. T. spinulosa occurs not uncommonly in the shelly 

 bed of the Dogger at Blue Wyke, also in the Ironstone of Glaizedale, associated with T. 

 denticidata, Ag.,'and T. V. costata, Lye. Specimens more or less imperfect also occur rarely 

 in the Supra-Liassic Sands at Frocester Hill, Gloucestershire. The localities mentioned by 

 Agassiz for his T. tuberculata do not define its geological position clearly in Southern 

 Germany, but, from its association with T. costellata and T. pulchella, we may infer that 

 its position nearly agrees with that at Blue Wyke. 



Trigonia corallina, IT Orb. Plate III, figs. 7, 8, 9, 11 j Plate VIII, fig. 3. 



Trigonia corallina, JfOrbigmj. Prodrome de Paleont., vol. ii, 14th et., 1850, p. 16, 



No. 260. 

 — clavellata, var. Jurensis, Grewingk. Gest. u. Geolog. Livonia und Cour- 



land, Dorpat, 1864. 



" Espece voisine pour les pet its tubercles rapprocJte's d/i cotes du T. concentrica, mais 

 avec les cotes Men plus serrees, moins arque'es, I' area anale striee en travers.'' — 

 D' Orbigny. 



Shell ovately trigonal, convex ; umbones antero-mesial, not much elevated, incurved, 

 and somewhat obtuse, anterior side short and curved elliptically with the lower border, 

 posterior slope lengthened, its outline rather convex, its junction with the area is obtusely 

 angulated or somewhat rounded. The escutcheon is lengthened and depressed, its upper 

 border raised ; the area of moderate breadth, flattened, with three small imperfectly 

 developed tuberculated carinas ; it has irregular rugose plications posteally, which, near to 

 the umbones, become transverse narrow costellse. The other portion of the surface has 

 numerous rows of narrow, ridged, curved, costse ; their tubercles are small, irregular, and 

 unequal, closely arranged, becoming attenuated and imperfectly developed towards the 

 anteal extremities of the rows, which, at that portion of the valve, have but little regu- 

 larity and are but slightly curved. The young examples (Plate III, figs. 8, 9, 11) are from 

 the Coralline Oolite of Wiltshire, and were collected by the officers of the National 

 Geological Survey. The larger examples (Plate III, fig. 7, and Plate VIII, fig. 5) are from the 

 Coralline Oolite at Pickering. As a species it is distinguished from T. concentrica, Ag. 

 (' Trigon.,' p. 20, pi. 6, fig. 10), by its shorter figure, its ridge-like sub-serrated costse, which 

 have less curvature ; the area also with its anteal ridge-like costellse and rugose middle 

 and posteal portions is equally distinctive. 



Stratigrap Ideal position and localities. It occurs very sparingly in the Coralline Oolite 

 of Pickering associated with T. perlata, Ag., from which it is distinguished by its small 

 dimensions, by the much greater number of the rows of costa?, by their more horizontal 



