228 CAMBRO-SILURIAN FOSSILS. 



this writer gives no description of his species, as his figure gives 

 at least the differences noticed, and as Mr. Sowerhy has unfortu- 

 nately described a totally different Silurian species under the 

 same name, I think (although this latter should not retain the 

 name of L. lata) that it is better to give a distinct name to our 

 very abundant and distinctly marked species. The British spe- 

 cies most allied to this is the L. attenuata (Sow.), which however 

 is easily distinguished by its much longer trigonal, retrally nar- 

 rowed form, arising from the gradual passage of the sides into the 

 posterior lateral margins (without angulation), the very promi- 

 nent narrow gibbosity from the beaks, &c. The substance of the 

 shell is very thin, and the traces I have seen apparently of the 

 mesial ridge extend little more than one-third the length of the 

 shell. 



Extremely abundant in the greenish slates of Penmorfa, Tre- 

 madoc, N. Wales; rare in the schists E. of Nant y Groes S. of 

 Bala, N. Wales. 



[CoL University of Cambridge.) 



Lingula tenuigranulata (M^Coy). 



Sp. Char. Shell black, semielliptical ; sides parallel, abruptly 

 rounded to the wide, nearly straight front, gradually rounding 

 into the undefined arched posterior lateral margins, which unite 

 elliptically in front of the beak, the curve being rather wider 

 than a semicircle, in the small valve, but more elongate from 

 the projection of the considerably longer beak in the opposite 

 one ; valves with a moderate, flattened, triangular gibbosity, 

 widening from the beak to the front margin, from which the 

 sides slope rather abruptly to the margins, the greatest depth 

 being at about the middle of the length ; surface with irregular, 

 flattened, concentric laminar wrinkles, strongest on the sides, 

 nearly obsolete in the middle ; entire surface covered with ex- 

 tremely minute, close, regular, equal, sharply granular, longi- 

 tudinal, slightly undulated strise (about twenty-six in one line 

 in the middle of the shell), the intervening spaces between the 

 striae about equalHng the strise in width. Length (of shorter 

 valve) 1 inch 9 lines, proportional width -^■^^, depth -^^-q. 



This species far exceeds the Lingula quadrata (Eichwald) in 

 size, though that has hitherto been the largest species known ; it 

 is easily distinguished therefrom as well as from the L. granulata 

 (PhilL), to both of which it bears some resemblance, by the ex- 

 tremely minute granular lineation of the surface (which is quite 

 invisible to the naked eye, or with a lens of low power only giving 

 a dullness to the surface) and the semielKptical regular arch 

 formed by the union of the two posterior lateral margins of the 



