272 APPENDIX TO THE SUPPLEMENTS TO 



species of the genus are so variable that, even with a large series before us, it is very 

 often difficult to discover sufficiently distinctive characters between closely allied forms. 



33. Rhynchonella bilobata, S. S. Buckman. Dav., Appendix to Supplements, Vol. 



V, PI. XIX, figs. 18, 18 a— c, 19, 

 19 a, b. 



Rhynchonella bilobata, S. S. Buckman. The Brach. from the Inf. Ool. of 



Dorset, Proc. Dorset Nat. Hist. 

 Club, vol. iv, p. 50, 1882. 



Shell triangular, wider than long, widest and broadly rounded anteriorly, tapering 

 posteriorly, sides curved. Dorsal valve slightly convex, flattened, and longitudinally 

 divided by a deepish furrow into two rounded lobes, which slope inwardly towards the 

 median groove. At a short distance from the margin the lateral portions of the shell 

 bend abruptly inwards at right angles to meet the margin of the opposite valve. Ventral 

 valve regularly convex, lateral portions, near the edge, bent at right angles so as to meet 

 the margin of the dorsal valve ; beak small, gently incurved, and much produced over 

 the smaller valve. Eoramen situated, under the angular extremity of the beak 

 and laterally margined by small deltidial plates. Surface of the valves smooth to within 

 a short distance from the margin where ten or twelve short ribs occupy the front and 

 lateral margins of the valves. Front margin much thickened. 

 Length 5, breadth 6, depth 3 lines. 



Obs. — We are indebted to Mr. S. S. Buckman for the discovery of this very 

 remarkable and well-characterised species, of which he obtained seven or eight ex- 

 amples from the Inferior Oolite zone of Am. Sowerbyi, at Bradford-Abbas in Dorsetshire, 

 and from near Corton Denham in Somersetshire. Some specimens are broader anteriorly, 

 and the marginal ribs are more developed in some examples than in others. No regular 

 ribs are seen in some specimens, only a little notching at the margin. It differs from B/t. 

 trifjona, Quenstedt, on account of the deep, narrow furrow in the dorsal valve, as well as 

 by the shortness of its ribs. 



34. Rhynchonella Dundriensis, S. S. Buckman. Appendix to Vol. I, PI. A, fig. 28. 



Appendix to Supplements, Vol. 

 V, PI. XIX, fig. 20, 20 a. 



Rhynchonella, sp., Dav. Ool. Mon., Appendix to vol. i, pi. a, fig. 28, 1855. 



Dundriensis, S. S. Buckman. Proceed. Dorset Nat. Hist. Club, vol. 

 iv, p. 43, 1882. 



