CLAVELLATJB. 47 



Shell ovately oblong, depressed, umbones antero-mesial, small, pointed and slightly 

 recurved, anterior and posterior borders curved elliptically ; posterior border lengthened, 

 its superior portion straight, and slightly sloping ; escutcheon lengthened, narrow, slightly 

 excavated, its outer border raised ; area moderately wide, flattened, transversely irre- 

 gularly striated, but usually delicately impressed, with a slight median furrow, and 

 bounded by two small, minutely tuberculated carina?. The other portion of the shell has 

 a numerous series (14 posteally) of regular curved and nearly horizontal small tuber- 

 culated costae, which are very delicate and minutely knotted anteally, directed from the 

 border slightly downwards to the middle of the valve ; posteally the costae are somewhat 

 larger, and more distinctly tuberculated ; the tubercles enlarge towards the carina, which 

 they meet at a right angle in the few last formed costae ; all the tubercles are depressed, 

 and very few are separated in the rows ; anteally there are one or two supplementary or 

 intercalated costae, the posteal terminations of which are about the middle of the valve. 



The aspect of this little species is peculiar, and its several features, although minute, 

 are very persistent ; few specimens exceed thirteen lines in length, and the greater number 

 do not exceed ten lines ; they were very gregarious, the disunited valves are profusely 

 scattered in a thin layer over the slabs of Stonesfield Slate at numerous localities in 

 Oxfordshire and Gloucestershire ; the shell substance is rarely preserved, but the im- 

 pressions in the soft sandy shale exhibit perfectly all the more delicate features of the 

 species. It appears to be entirely absent in the shelly beds of the Great Oolite. 



Its figure is more lengthened than T. Moretoni, its costa are more numerous, the area 

 has never the coarse rugose aspect of that species, and the entire ornamentation is much 

 more minute and delicate ; other Trigoniae are more remotely allied. A large example has 

 the height 10^ lines, length 14 lines. 



Trigonia Moretoni, Mor. and Lye. Plate II, figs. 4, 5, 7, 8 ; Plate IV, fig. 6. 



Trigonia Moretoni, Mor. and Lye. Gr. Ool. Monogr. Pal. Soc, 1853, p. 57, tab. v, 



figs. 19, 19 a. 



— — Morris. Catal., 1854, p. 228. 



— — Rigauas et Sauvage. Descr. de Quelq. Esp. Nouv. de l'Etage 



Bathonien, extr. du vol. iii, Mem. de la 

 Soc. Academ. de Boulogne, 1867, p. 19. 



— — Sharp. Oolites of Northamptonshire, p. 383 ; Quart. Jour. Geol. 



Soc, August, 1870. 

 — CLAPENSIS, O. Terquem et E. Jourdy. Monog. de l'Etage Bathonien dans 



le Depart, dela Mozelle, Mem. Soc. 

 Geol. de France, 2 ser., 1869, torn. 

 9, PL II, figs. 1, 2, 3, 4. 



Shell ovately trigonal, rather depressed, umbones antero-mesial, elevated and only 

 slightly recurved ; anterior border moderately produced and curved elliptically with the 



