76 BRITISH OOLITIC AND LIASIC BRACHIOPODA. 



was found, by its regular and more indented plaits proceeding from the beak and umbo, 

 while in B. ring ens they appear at a greater distance. It differs also in general shape, as 

 may easily be perceived on comparing the respective figures of these species. It bears, 

 however, some resemblance to the above-named form by its sinus being likewise strongly 

 marked by a central longitudinal line. 



Plate XIV, fig. 17. From a specimen in the collection of the Museum of Practical 



Geology, 

 fig. 17 aJc . Enlarged illustrations. 



69. Rhynchonella acuta, Sow. Sp. Plate XIV, figs. 8, 9. 



Teuebratula acuta, Sowerby. Min. Con., 1818, vol. ii, p. 115, tab. 151, figs. 1, 2. 



— — Schloth. System. Ver. der Petref., 1832. 



— — Beshayes, 1836. Nouv. Ed. de Lamarck, vol. vii, No. 69, p. 353. 



— — V. Buck. Uber Terebrateln, 1834 ; et Mem. Soc. Geol. de France, 



1838, vol. iii, l re ser., p. 142, pi. xiv, fig. 11. 



— — Phillips, 1835. Geol. of York., pi. xiii, fig. 25. 



— — Beslongchamps, 1837. Soc. Linn, de Normandie, p. 30. 



— — Morris, 1843. Catalogue. 



— — Bronn, 1848. Index Pal., p. 1228; figured also in tbe 'Encyc. 



Metb.,' pi. 255, fig. 7. 



Diagnosis. Shell inequivalved, more or less triangular, wider than long, the smaller 

 valve rising in an almost straight line from the umbo to the margin, and forming a large 

 central acutangular plait, the sides sloping rapidly in the manner of a roof ; two or three 

 other smaller lateral costse exist on each side, the first of which is larger than the other two, 

 andean be traced almost from the umbo; in the perforated valve a deep sinus is seen, which 

 corresponds with the central plait of smaller valve; there exists also three lateral costse. The 

 beak is small, acute, and not much produced, with foramen entirely surrounded by the 

 deltidial plates ; margin of the valves deeply sinuated, hinge margin of larger valve not much 

 indenting the smaller one ; structure unpunctuated. Length 10, width 13, depth 11 lines. 



Obs. B. acuta occurs abundantly in the Marlstone, or Middle Lias of Ilminster, in 

 Yorkshire, Wilton Castle, Rilsdale, &c. On the continent it is met with at Landes, Vieux 

 Pont, Evrecy, &c, in Normandy, and does not appear to vary much in shape, being always 

 easily recognised. 



In the Oxford Clay of Koroskovo, near Moscow, in Russia, we find a small shell, which 

 received from Fisher, in 1809, the name of Bhjnchonella loxia, on which type the genus 

 appears to have been established later; 1843 the same author gave to the same shell the name 

 of Aptyca: it bears the greatest possible outward resemblance to B. acuta, of Sowerby; but, 

 as stated by M. D'Orbigny, can be distinguished 1 by a more marked longitudinal groove in 

 the sinus of the larger valve, visible especially at its extremity, its surface being everywhere 



1 Geology of Russia, t. ii, p. 482, pi. xlii, fig. 22—26. 



