MODIOLA. 



CONCHIFERA. 



171 



rounded and obtuse ; surface smooth ; liinge destitute of 

 teeth. 



Tlio Lower Greensand, Pulborough and Blackdown. 



5. The JIvTiLus LANCEOLATUs. — Spcar-shapcd Mytilus, 

 pi. LXXI. fiir. 2. 



M. lanccohitus. Sowcrby, V. p. 5,5, pi. 439, fig. 2. 



Lanceolate, a little curved, smooth ; beaks acute ; disk carin- 

 ated, smooth ; posterior side flat ; anterior side svreeping 

 regularly from the beaks to the front ; within each beak a 

 lamellar tooth. 



Greensand, Parkhani and Lyme Regis. 



fi. Mytilcs subl.evis. — The Half-smooth Mytilus, pi. 

 LXXI. fig. 2fi. 



3/. lubltwis. Sowerby, V. p. 5G, pi. 439, fig. 3. 



Oblong, triangular, somewhat arcuated ; beaks acute ; disk 

 obscurely carinated ; front straight ; hinge-lino parallel, ex- 

 tending to half the length of the shell, where it is a little 

 fiattened ; surface with pretty strong lines of growth. 



The Cornbrash, Felmershani, Bedfordshire. 



7. Mytilus pectinatus. — The Toothed Mytilus, pi. LXXL 

 fig. 18. 



M. pectinatus. Sowerby, TIL p. 147, pi. 282. 



Rather ([uadrangular, slightly arcuated ; oblong and gibbose ; 

 beaks produced; front straight; surface with longitudinal, 

 rather deep, very regular striie, which increase in number as 

 they diverge towards the front or base of the valves, from 

 which two obtuse angles emanate, giving a quadrangular form 

 to the shell. 



The Kimraeridge Clay, Weymouth. 



8. JIytilus in^equivalvis. — The Unequal- valved Mytilus, 

 ].!. LXXL figs. 6, 7. 



M. inaequitalcis. Sowerby, Geo. Trans. 2d Series, IV. 

 p. 342, pi. 17, fig. 16. 



Sub-triangular ; beaks nearly central, broad, sub-compressed; 

 one valve considerably flatter than the other ; surface smooth, 

 with faint concentric lines of growth. 



The Greensand, Blackdown. 



9. MvTiLrs PR^LOJJGUs. — The Lengthened Mytilus, pi. 

 LXXL figs, f), 10. 



M. praelonms. Sowerby, Geo. Tr. 2d Ser. IV. p. 342, pi. 

 17, fig. 15. 



Considerably elongated, narrow, a little arcuated and carinat- 

 ed ; hinge-lino nearly straight and rather long, destitute of 

 teeth ; surface smooth ; substance of the shell very thick. 



The Greensand, Blackdown. 



10. Mytilus tridens. — The Three-toothed Mytilus, pi. 

 LXXI. figs. ~, 8. 



M. trhlem. Sowerby, Geo. Tr. 2d Ser. IV. p. 342, pi. 17, 

 fig. 14, II). Jlin. Conch, p. 55, pi. 439, fig. 1. 



Elongated, convex ; carinated ; beaks acute ; hinge-line 

 nearly straight ; hinge with three unequal teeth ; posterior side 

 almost even ; surface very smooth. 



The Greensand, Blackdown. 



11. Mytilis Lyellii. — Lyell's Jfytilns, pi. LXXI. f. 27. 

 M. Lyellii. Sowerby, Geo. Tr. 2d Ser. IV. p. 346, pi. 21, 



fig. 18. 



Oblong-ovate ; a little flattened, especially towards the 

 front ; much narrowed above and expanded below ; beaks very 

 sharp, beneath which the valves are inflated. 



The Weald, Battle and Pounceford. 



12. Mytilus cuneatus. — The Wedge-shaped Mytilus, pi. 

 LXXI. fig. 14. 



M. cuneatus. Phillips, Geo. York, I. pi. 11, fig. 21. 



Somewhat wedge-shaped, short ; posterior side nearlv 

 straight, anterior side much produced ; beaks obtuse ; surface 

 smooth, with rather wide striaj occupying the lower half of the 

 valves. 



The Inferior Oolite, Glaizedale, Yorkshire. 



13. Mytilus cinctus. — The Girdled Mytilus. 



M. cinctus. Portlock, Geo. Rep. p. 426, pi. 25, figs. 5, 6. 



Considerably elongated, narrowed above, with rather acute 

 beaks, and expanded and ronnded below ; hinge-line a little 

 curved; surface smooth, with "fine thread-like stria), proceeding 

 from the apex, first straight, and then curving back over the 

 back concentrically to the rounded front, jyroceed straight up 

 to the levelled line of the apex, or upper line of the wing." 



The Silurian Strata, Fermanagh and Lisbellaw Schists, 

 Tyrone. 



14. Mytilus semi-rugatus. — The Semi-ragged Mytilus. 

 M. semi-rugatus. Portlock, Geo. Rep. p. 430, pi. 25 A, f. 7- 

 " Wide, rudely trigonal ; beak sharp, front wide, and usually 



more or less twisted or distorted ; for about one-third of the 

 length from the beak transversely wrinkled ; longitudinally 

 striated or very finely costated. In 'some specimens the shell 

 is much more contorted or arched." 



Silurian Strata, Fermanagh, Tyrone, Ireland. 



15. Mytilus triangularis. — The Triangular Mytilus. 

 M. triangularis. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, 



fig. 16. 



Elongated, sub-triangular, slightly oblique ; sub- compressed ; 

 a flat oblique ridge running from the apex to nearly the basal 

 margin ; beaks obtuse, surface smooth. 



The Coal Measures, Coalbrook Dale. 



16. Mytilus Danmoniensis. — The Devonshire Mytilus. 

 M. Danmoniensis. Phillips, Pal. Fos. p. 37, pi. 17, fig. 61. 

 Much elongated and oval ; hinge-line short, straight, and 



prominent ; base broad and flat. 

 Devonian Shales, Newton Bushel. 



17. Mytilus .equilatus. — The Equal-sided Mytilus, pi. 

 LXXI. fig. 15. 



M. antiquorum. Young shell, Sowerby, III. pi. 275, f. 3. 



Oblong-oval, sub-compressed ; sides broad, nearly equal ; 

 hinge-line occupying almost half the length of the shell, and 

 nearly straight ; beaks obtuse, nearly central ; surface smooth, 

 with remote, slightly-marked lines of growth. 



The Sufiolk Crag, Ipswich. 



Gen us XXXV.— JIODIOLA.— Zawarc/fc. 



Shell sub-transverse, equivaJve, regular, oblique ; form ob- 

 long, somewhat wedgc-.shaped, and generally inequilateral ; 

 anterior side very small and obtuse ; posterior side rounded 

 and closed ; anterior margin slightly gaping for the passage of 

 the byssus, and forming, with the base, a line oblique to the 

 dorsal one ; beaks nearly lateral ; outside covered with a 

 strong horny epidermis ; hinge without teeth ; ligament 

 elongated, and sub-external ; two muscular impressions, the 

 posterior one large, sub-lateral, elongated, and irregular; the 



