RHYNCHONELLA. 227 



Cyutina septosa, Phillips (p. 68). Plate XIV, figs. 1 — 10; Plate XV, figs. 1, 2; and 



Plate LI, fig. 17. 



When publishing my description and figures of this interesting species I expressed a 

 regret that all my efforts had proved ineffectual in making out the interior characters of the 

 dorsal valve. Since then, thanks to the continued and zealous exertions of my inde- 

 fatigable friend Mr. Burrow, the internal cast of the dorsal valve was discovered (PI. LI, 

 fig. 17), showing that the muscular impressions (anterior and posterior divisions of the 

 adductor or occlusor muscle) were similarly arranged to those of Spirifera, and that there 

 does not exist in that valve any septa, as in Pentamerus, a fact I also mentioned while 

 describing M'Coy's so-termed Pentamerus carbonarius. 



Rhynchonella (pp. 89 — 112). 



Eight or nine species have been provisionally retained ; but the claims of Rh. cordifor- 

 mis have not been satisfactorily established, and of Rh. (?) gregaria, but two imperfect valves 

 have come under my examination. Rhynchonella trilatera is a rare shell, but several 

 specimens have been recently found by Mr. Burrow near Settle, in Yorkshire, and some 

 others by Mr. Carrington in the Limestone of Wetton, in Staffordshire. Rh. (?) nana, and 

 R. semisulcata are at present by far too doubtful to deserve more than a passing notice. 

 When describing and illustrating Rh. pleurodon, I was much puzzled with a large Rhyn- 

 chonella (PI. XXIII, fig. 22), which appeared to me to differ from the last-named shell in 

 several particulars, and which I then doubtfully and provisionally left under R. pleurodon. 



> 



Rhynchonella (?) Carringtoniana, Dav. Plate XXIII, fig. 22 ; and Plate LIII, 

 figs. 1, 2. 



Sp. Char. Shell transversely oval, valves almost equally deep. Dorsal valve convex, 

 with a broad mesial fold apparent only on the anterior half of the shell, where it is 

 rarely very much elevated. About thirty-two or thirty-four radiating, rounded, simple 

 ribs ornament this valve, of which from six to seven occupy the fold. A r entral valve 

 longitudinally divided by a broad sinus, and marked with about the same number of ribs 

 as in the opposite valve. Beak small and incurved ; dimensions variable. 

 Length 15, breadth 19, depth 11 lines. 



Obs. While illustrating Rh. pleurodon in PI. XXIII of the present Monograph, I 

 received from Mr. Parker, of Manchester, the loan of a large shell, fig. 22 of the same 

 plate, which he had obtained from the Carboniferous Limestone of Twiston, in Lanca- 

 shire. This shell appeared to differ so much from the many specimens of R. pleurodon, in 

 my possession, that I did not venture to refer it positively to any known species. Since 



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