200 SUPPLEMENT TO THE BRITISH 



188. Rhynchonella sub-tetraedra. Dav., Ool. Mon., p. 95, PI. XVI, figs. 9 — 12. 



Nothing new. It varies very much in shape, and in the number of its ribs. Fine 

 examples occur in the Inferior Oolite of Dundry, and it has been met with abundantly by 

 Professor Buckman and Mr. Darell Stephens in the same formation at Bradford Abbas 

 and its neighbourhood. It also occurs in the Cheltenham district. 



189. Rhynchonella amalthei, Quenstedt. Sup., PI. XXVIII, figs. 18, 19, 20, 21 ? 



Terebratula amalthet, Quenstedt. Handbuch der Pet., p. 453, tab. xxxvi, fig. 17, 



1831. 

 Rhynchonella — Oppel. Die Jura-Formation, p. 188, 1856. 

 Terebratula — Quenstedt. Petrefactenkunde ; Deutschlands Brachiopoden, 



p. 65, tab. xxxvii, figs. 154 — 161, 1871. 



Shell small, sometimes almost globular, about as wide as long; valves moderately or 

 very much convex, even gibbous. Dorsal valve uniformly convex to about half its length, 

 after which a slightly raised mesial fold, more or less defined, with small lateral slopes, 

 extends to the front. Ventral valve rather less deep than the opposite one, with a wide, 

 moderately deep mesial fold, commencing at about half the length of the valve from the 

 beak. Beak small, much incurved, with a small circular foramen under its angular 

 extremity, margined by two narrow deltidial plates. Surface of each valve ornamented with 

 about thirty small, simple, radiating ribs, of which about six or seven occupy the fold and 

 sinus, and become wider and stronger as they approach the front. Proportions variable. 

 Length and width about 5 lines, depth 4. 



Some specimens are not so deep, and others have slightly exceeded the proportions 

 here given. 



05s. — This small shell varies considerably in the respective depth of its valves, as well 

 as in the elevation of its mesial fold ; this last is clearly defined in the larger number of 

 specimens, but in some examples, and especially when the valves are very convex, the 

 fold becomes hardly perceptible, and the valve is uniformly convex. Rh. amalthei has 

 been well described and figured by Quenstedt, and our British examples agree with the 

 German type. Dr. D. Brauns, in ' Der untere Jura in nordwestichen Deutschland,' 

 places Rh. amalthei among his synonyms oi'Rh. tetraedra ; but I think this is a 

 mistake, although I am ready to admit that some young specimens of the last-named 

 shell approach much to Quenstedt's species. Rh. amalthei, however, remains the small 

 shell we have described, while Rh. tetraedra attains to comparatively larger dimensions. 

 I am indebted to Dr. Fraas for some typical German specimens, which agreed in every 

 particular with some of those found in England. 



