THE BRITISH FOSSIL BRACHIOPODA. 273 



Shell obscurely sub-pentagonal, wider than long. Dorsal valve convex, with a wide, 

 slightly prominent mesial fold, rising at about the middle of the valve and extending 

 to the front. Ventral valve more convex than the opposite one, with a shallow sinus 

 commencing at about half the length of the valve ; beak incurved, with a circular foramen 

 under its angular extremity, margined by deltidial plates ; beak ridges sharply defined. 

 Surface of valves covered with a large number of fine radiating ribs or striations. 

 Length 1 inch, breadth 1| inch, depth 7 lines. 



Obs. — In 1854 I received from the Bristol Museum the loan of a very perfect adult 

 example of the shell under description, and figured it in Vol. I, Appendix, PI. A, fig. 28, 

 without giving it a specific name. It was said to have been obtained from the Inferior 

 Oolite at Dundrey. Since then two or three young specimens of the same species have 

 been found by Prof. Buckman and by Mr. T. C. Maggs in the Inferior Oolite at 

 Bradford-Abbas in Dorsetshire. Mr. S. S. Buckman gave it the specific name of 

 Dundriensis. When young the dorsal valve is nearly flat. This seems to be a good 

 species and remarkable on account of the large number of small ribs that cover its 

 surface. 



35. Rhtnchonella poetlajjdica, Blake. Dav., Appendix to Supplements, Vol. V, 



PI. XX, figs. 6, 6 a, b, c. 



Rhynchonella portlandica, Blake. Quart. Journ. Geol. Soc, vol. xxxvi, p. 234, 



pi. x, fig. 8, 1880. 



Shell subpentagonal, about as wide as long. Dorsal valve very convex, with a 

 prominent angular mesial fold and wide lateral slopes ; folds variable in shape, sometimes 

 bifid or even trifid ; on each of the lateral lobes of the valve are three or four shorter 

 ribs. Ventral valve less deep than the dorsal one, with a large mesial angular sinus, in 

 the middle of which are sometimes one or two shorter ribs, and three or four on its 

 lateral lobes ; beak incurved with a small circular foramen under its angular extremity. 

 Surface of the valves marked with close concentric lines. 

 Length 5, breadth 5 lines. 



Obs. — Prof. Blake found this small species in the lower part of the Portland Sand at 

 Black Ven, Portland, and less common in corresponding beds at St. Alban's Head. 

 Prof. Blake seems uncertain whether his species is distinct from Rh. subvariabilis from 

 the Kimmeridge Clay of Pottern, Wilts, which is the equivalent of the Swindon and 

 Hartwell Clays, and therefore very little removed in time from the deposit whence his 

 Rh. portlandica was derived. Rh. siibvariabilis is a larger shell, and I have seen too few 

 examples of either species to be able to say if they are really the same. Prof. Blake's 

 figures of Rh. portlandica approach also much in shape to Rh. acuta. 



