200 SUPPLEMENT TO THE 



Rhynchonella Balcletchiensis, Bav. Sil. Sup., PI. X, figs. 15, IG ; and PI. XI, 



fig. 23. 



Since describing this well-marked species at p. 160 of this Supplement, Mrs. R. 

 Gray has procured some remarkably perfect bivalve examples from the Llandeilo at 

 Minuntion, in Ayrshire. 



In the dorsal valve the mesial fold commences to rise at a short distance from the 

 umbo, is large, roof shaped, and more acute in some specimens than in others. In 

 some examples it is simple and angular throughout, in others slightly biplicated on its 

 anterior third. The lateral lobes of the shell are either nearly smooth or with numerous 

 small and but slightly prominent ribs. The ventral valve has been already described. 

 Some of the Minuntion specimens measured 6 lines in length by 7 in breadth. 



128. Rhynchonella cuneatella, Bav. Sil. Sup., PI. X, fig. 11. 



Shell small, cuneiform or triangular, broadest anteriorly, tapering posteriorly, longer 

 than wide ; dorsal valve very moderately convex, slightly flattened, smooth to about 

 two thirds of its length, anterior third with about six short, strongish ribs, of which four 

 form a comparatively broad and slight prominent fold ; ventral valve moderately convex, 

 beak slightly incurved with a small circular foramen, surface smooth for two thirds of its 

 length, with about five short ribs rising near the front. 

 Length 3, width 2^, depth 1^ hues. 



Ohs. — Since I alluded to this small shell in the last paragraph at p. 153 of this 

 Supplement, as being perhaps referable to Bh. cuneata, Mrs. R. Gray has collected 

 several more examples from the Balcletchie (Llandeilo) Conglomerate of Ayrshire, and 

 they all were small and similar to the one figured in PI. X of this Supplement. All 

 the specimens were quite smooth to about two thirds or more of their length, and I am 

 now satisfied that they cannot be looked upon as young ages of Bh. cuneata, which is 

 at all ages ribbed throughout. I therefore propose to distinguish this small species by 

 a separate name. In some examples of Bh. cuneatella the anterior short ribs are hardly 

 visible. It is only by correcting and adding to descriptions of imperfectly made out 

 species, when suitable material turns up, that we may hope ultimately to arrive at 

 something definite. 



