210 SUPPLEMENT TO THE BRITISH 



the main ironstone seam, the only species of the genus occurring therein. The smallest 

 specimen showing plications is three quarters of an inch broad, but still retains the 

 depressed shape of the juvenile examples. Examples of Rh. tetraedra at this stage have 

 already been described, whilst young specimens of Rh. acuta, with a diameter of three 

 eighths of an inch, present a strong mesial fold and lateral plications. I cannot agree witl 

 Simpson, who considers the species related to Rh. tetraedra rather than Rh. variabilis, 

 and still less with Brauns, who places it with Rh. cynocephala under Rh. acuta." 



" Geological position. — Zone of Am. spinatus. Very abundant in the shaly ironstone 

 called the c Cockle Band,' at the base of the Cleveland Main Seam at Eston ; also in the 

 Main Seam, Eston, Upleatham, Straithes, Runswick, Hawsker, &c." 



213. Var. Radstockiensis, Dav. Ool. Mon., PI. XVI, figs. 4 and 6. 



This is a variety of Rh. lineata, intermediate in size and shape between Rh. variabilis 

 and Rh. lineata. It occurs plentifully in the Middle Lias, at Clandown quarries, 

 Radstock, and Churchdown in Gloucestershire. It is a squarer, more regularly 

 convex, and smaller shell than Rh. lineata proper, and its young are very different from 

 those of the typical form. 



It has generally three ribs on the mesial fold, and five on each of the lateral lobes. 



It rarely exceeds, or even attains, 10 lines in length, by the same in width, and 8 in 

 depth. In PI. XV of my Monograph of Oolitic and Liassic species I have given two figures 

 showing the characters of this variety. 



214. Rhynchonella oxynoti, Quenstedt. Dav., Sup., PI. XXVIII, figs. 37, 38. 



Terebratula oxynoti, Quenstedt. Handbuch der Petref., p. 451, pi. xxxvi, figs. 4, 



5, 1851. 

 _ _ Quenstedt. Der Jura, p. 112, tab. xiii, figs. 22, 23, 1858. 



— — Quenstedt. Die Brachiopoden Pet. Deuts., pi. xxxvii, figs. 



60, 61, 1871. 

 Rhynchonella — R. Tate. Additions to the List of Brach. from the Sec. Rocks, 



Geol. Mag., vol. vi, p. 553, 1869. 



Shell small, subpentagonal, slightly broader than long, widest anteriorly, tapering 

 posteriorly to a pointed beak. Valves moderately convex ; dorsal valve smooth to about 

 one third or more of its length from the umbo, afterwards divided into three lobes ; the 

 central one forms a sharply defined mesial fold with wide lateral slopes ; two or three 

 small longitudinal ribs cover the upper portion of the fold, while three or four short and 



