JURASSIC AND TRIASSIC BRACHIOPODA. 17 i 



slightly depressed along the middle to a short distance ; ventral valve somewhat carinated ; 

 beak much incurved, and truncated by a small circular foramen very slightly separated 

 from the hinge-line by small deltidial plates j beak-ridges sharply defined ; surface 

 smooth, marked by numerous strong concentric lines of growth. Length 16, width 11, 

 depth 11 lines. Young specimens are elongated oval. (Sup., PI. XXIV, figs. 14, 15). 

 Obs. — Mr. E. Deslongcharaps considers this shell to be specifically distinct from W. 

 ornithocephala. In England it occurs, with W. ornithocephala, in the Fuller's Earth 

 Oolite of Powerstock, near Bridport, and in the Inferior Oolite of Charlcombe, near Bath. 

 Mr. Deslongchamps states that the species is very abundant in the White Oolite near 

 Caen, and that it is likewise found in the Puller's Earth and Inferior Oolite in 

 Calvados, Sarthe &c. Some specimens seem nearly allied to W. ornithocephala. 



Waldheimia obovata, W. digona, and W. bucculenta. 



These three species seem to be so intimately related as to form a small group, to 

 which might be added several others, not only from the Jurassic rocks, but likewise from 

 the Cretaceous strata. 



150. Waldheimia obovata Sow., sp. Dav., Ool. Mon./p. 39, PI. V, fig. 14 — 17, and 



PI. VII, fig. 5 ; Sup., PI. XXII, figs. 10, 11. 



Teeebratula digona, var. Smith. Strata Identified, p. 26, pi. ix, Cornbrash. (Not 



T. digona, Sow.) 1816. 



Waldheimia obovata, Walker and Hudleston. Communications to Monthly 



Meetings of the Yorkshire Phil. Soc, 1877. 



Since describing this species at p. 39 of my Monograph, Mr. J. F. Walker has 

 obtained a large number of finely preserved specimens from the Cornbrash of Yaxley or 

 Stilton, near Peterborough, also from Cirencester. He has been able to point out two or 

 three tolerably persistent varieties, which he considers desirable to characterise by dis- 

 tinctive denominations. 



The typical form (Ool. Mon. PL V, figs. 14—16 ; and Sup., PI. XXII, fig. 10) is 

 more or less sub-pentagonal, almost as wide as long, with a wide straight front. Some 

 malformations show a tendency to rudimentary plications along the frontal line, but these 

 folds do not extend to any distance on either valve. Some examples (Sup., PI. XXII, 

 fig. 10) become very convex, so as to almost simulate T. spharoidalis. Por this last named 

 variation Mr. J. F. Walker proposes the subordinate designation perobovata. In addition 



