80 BRITISH OOLITIC AND LIASIC BRACHIOPODA. 



are mistaken in some of their synonyms ; thus Prof. Bronn is disposed to consider 

 B. cynocephala, as perhaps the same, while M. C. Rouillier places B. acuta of Sow., as 

 a simple variation of triplicata with one plait, and bidcns as a variety with two on the 

 mesial fold, overlooking the important character distinguishing the Sowerby type, viz., 

 that the central and only plait forms an elevated curve from the umbo to its extremity, 

 so that at the front the plait becomes not only the highest part of the shell, but is even 

 frequently bent upwards, while in triplicata the plaits bend downwards long before having 

 reached the frontal margin. A single glance at the respective figures will point out the 

 difference ; Mr. Morris has fallen into the same error, since he considers B. cynocephala to 

 be Professor Phillips's T. bidens. Through the kindness of Mr. Riply of Whitby, I have 

 been enabled to examine the Professor's types, and a numerous suit of specimens illus- 

 trating some of its numberless varieties. 



We can hardly believe, with Professor Bronn, T. variabilis of Schlotheim to be a 

 specimen of B. rimosa ; it presents none of the characters of that shell. B. variabilis 

 belongs to the Middle and Upper Lias, the var. triplicata and bidens of Phillips being 

 stated by that author to be peculiar to the Marlstone and Ironstone series, 1 PI. XVI, 

 figs. 1 and 3, illustrating the Professor's types. It is common, likewise, to the Lias of 

 several other British localities, such as near Ilminster and Radstock, where the shell 

 often assumes a considerable degree of variation, as may be perceived in PL XIV, figs. 4 

 and 6, and PI. XV, figs. 8, 9, 10. These last are more like the type of the species ac- 

 cording to Schlotheim's figure, where the frontal margin has become considerably thickened, 

 they are exceptions to the general form. Pigs. 4 and 6 of PI. XVI, are also more 

 convex and compressed laterally, but we can trace all the intermediate passages uniting 

 these extreme points of variation. A dwarfish variety is likewise met with in the Lias of 

 Stonehouse, near Stroud, PI. XVI, figs. 2 and 5. On the Continent it has been collected 

 in many localities, presenting all the variations found in England, and is not rare in the 

 Upper Lias of Croisilles and Subles, near Caen, and Bayeux in Normandy, also at Amberg, 

 and I have specimens sent me by Dr. Krantz, from Kirchum, in Wurtemberg, and from 

 Khoroschova, near Moscow, in Russia. 



72. Rhynchonella subvauiabilis, Bav. Plate XV, fig. 7; and Plate XVIII, fig. 11. 



Diagnosis. Shell transversely irregularly oval, wider than long; beak not much 

 produced, acute and slightly recurved, leaving a flat false area between its ridges and the 

 hinge margin; foramen small, almost entirely surrounded by the cleltidium, a small portion 

 only being completed by the umbo. Valves convex, ornamented by 9 or 11 plaits, 



1 The specimens of this species from the Ironstone bands rarely preserve the shells, which present 

 a more or less advanced state of decomposition, exhibiting those longitudinal asbestoid fibres mentioned by 

 M. C. Rouillier, in his ' Etudes Progressives sur la Palaeontologie des Env. de Moscou,' 1847- 



