BRITISH SILURIAN BRACHIOPODA. 151 



(Hisinger). At all ages it presents the same appearance, and is a well-marked species. 

 It occurs in the Lower Ludlow, but is more plentiful in the Upper-Wenlock Shales of 

 Shropshire, where many examples were procured by Mr. G. Maw from his washings of 

 Wenlock Shales from under Benthall Edge, and from above Tickwood and Farnley 

 Dingle. It occurs also in the Wenlock Limestone at Dudley, and in Wenlock Shales at 

 Falfield near Totworth. It is a most beautifully sculptured shell. 



It is probable that Sowerby's Ter. hidentata (' Sil. Sys.,' pi. xiii, fig. 13 a) has 

 been drawn from a large example of Hisinger's T. hidentata, but of this I am not 

 certain. In most specimens of the shell the two median ribs in the dorsal valve come 

 very close to each other. The small shell figured by Quenstedt in pi. xxxv of his ' Petre- 

 factenkunde ' is certainly Hisinger's T. hidentata^ and not a young Bh. borealis. 



35. Rhynchonella diodonta, Dalman, sp. Dav., Sil. Sup., PI. X, fig. 4. 



Terebkatula diodonta, Dalman. Vet. Akad. Handl., p. ]42, pi. vi, fig. 4, 1828. 



— — Hisinger . Icon. Petref. Svec, p. 81, pi. xxiii, fig. 6, 1837. 



In external shape and general appearance this species (?) much approaches to that of 

 BJi. bidentata, of which some Palaeontologists would consider it to be the adult. At 

 one time I was myself inclined to follow in the same view, but after having had so many 

 specimens of the true Bh. bidentata under examination, I began to doubt the propriety of 

 considering it the same as Hisinger's species. 



Dalman describes his shell : — " T. testa radiatim profunde plicato-sulcata, sulcis 

 transversim undulato-striatis ; valvge majoris sinu profundo, unicostato, apice incumbente, 

 bifido." 



It measures : length 6, width 7, depth 4 lines, and is consequently very much larger 

 than the largest specimens of Bh. bidentata that have come to my notice. Then it has 

 five ribs on each lateral portion of its valves, instead of the three comparatively larger 

 ones in Bh. bidentata. 



Bh. diodonta occurs in the Wenlock Shales near Dudley, and in other places ; and is 

 quoted by Dalman and Hisinger from the Upper Silurian of Gothland and Klinteberg. 



36. Rhynchonella decemplicata, Sow. Dav., Sil. Mon., PI. XXIII, figs. 20 — 24, 



Sup., PI. XI, fig. 27. 



This is another small form, distinct though allied to Bh. bidentata and Bh. diodonta. 

 It is well described and figured at p. 177 of my ' Silurian Monograph.' It has two large 



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