SPIRIFERIDtE. 



89 



Spirifera plicatella, var. globosa, Salter. PI. IX, figs. 7, 8. 



Spieifer plicatellus, var. globosus, Salter. Mem. Geol. Surv., vol. ii, part i, 



p. 382. 1848. 



Spihifera plicatella, var. globosa, Lindstnm. Proceed. Roy. Acad. Sc. Stockholm, 



1860, p. 158. 



The shell of this variety is, according to ]\Ir. Salter, " about as wide, or a little wider 

 than long ; hinge-line veiy short ; beaks approximate ; furrows none ; very gibbous it 

 is the variety easily connected with Sjnrife?- radiatus, Sow. Indeed, there appears to be 

 little by which it can be distinguished from the true Sjpirifera radiata, except the greater 

 convexity or gibbosity of its valves and its finer striation. Two specimens measured — 

 Length 20, breadth 26, depth 15 lines. 

 „ 15, „ 17, „ 13 „ 



Spirifera MarUini, de Vern., is easily distinguishable from Sp. glohosa by its less 

 transverse shape, and by its great depth and square-like appearance. 



This variety is not rare in the Wenlock Limestone at Dudley ; and it occurs also in 

 the Island of Gothland.^ 



Spirifera bijugosa, M'Coy. PI. X, figs. 1 — 3. 



Spirifer bijugosus, WCoy. Synopsis Sil. Fobs. Ireland, p. 36, pi. iii, fig. 23, 1846. 

 — — Salter. Explanation of Sheets 160, 161, 171, and 172, Geol 



Surv. Ireland, p, 13, 1863. 



Spec. Char. Rotundato-quadrate, wider than long, valves more or less gibbous ; 

 hinge-line as long as the width of the shell. Dorsal valve rather less deep than the 

 opposite one ; mesial fold moderately wide ; smooth, and divided along the middle by a 

 deep hollow groove ; the remaining portions of the valve being covered with from twenty 

 to twenty-four obtusely angular, simple ribs, the whole crossed by numerous concentric 

 lines of growth. In the ventral valve the sinus is wide and concave, and extends from 

 the extremity of the beak to the front ; while the lateral portions of the valves are covered 

 with ribs, as in the opposite valve ; beak incurved, area about a couple of lines wide, 

 fissure triangular, and partly arched over by a pseudo-deltidium. A large specimen 

 measured — 



Length 12, width 14 lines. 



1 Herr Lindstrom informs me that he has seen Spirifera plicatella from the Upper Silurian rocks 

 in the neighbourhood of Christiania in Norway, accompanied by the following species — Spirifera elevafa, 

 Meristella tuinida, Atrypa reticularis. At. imbricata, Pentamerus oblongus, P. linguiferus, Rhjnchonella 

 cuneata, Rh. diodonta, Rh. nucida, Rh. sphcerica, Rh. Wihoni, Orthis canaliculata, 0. hybrida, 0. biforata, 

 Strophomena rhotnboidalis, St. pecten, Leptcena transversalis, and Ckonetes striatella : — a series which 

 must, says Mr. Salter, "represent our May Hill Sandstone." 



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