228 



COiNCHIFERA. 



MVA. 



Tribe I.— MYARIA. 



Ligament internal ; a broad, spoon-shaped tooth in each 

 valve, or in one only ; shell gaping at both sides, or at one 

 only. 



Genus LXII. — MYA. — Linnceus. 



Shell transverse, nearly equivalve, gaping at both extremi- 

 ties, but widest at the posterior end ; one valve with a large 

 compressed, dilated, spoon-shaped, vertically projecting tooth ; 

 the opposite valve destitute of teeth ; two lateral, distant, 

 muscular impressions, the anterior one narrow, and the poste- 

 rior one orbicular ; mantle muscular impression witli a large 

 sinus ; ligament internal, large, and fixed in the cavity of the 

 tooth, in one valve, and to a large sub-umbonal cicatrice in 

 the other. 



1. Mta rotundata. — The Rounded Mya, pi. XCII. f. 22. 

 M. rotundata. Sowerby, Silur. Syst. pt. II. p. 613, pi. 6, 



fig. 1. 



Shell transversely oblong, convex ; beaks obtuse, and situate 

 near the anterior side, which is separated by a concave space 

 from the middle of the valves ; posterior side rounded ; surface 

 wrinkled transversely. 



This species strongly resembles Cypricardia umlata, but will at once 

 be distinguished by its want of a lunette. 



From the Aymestry Limestone, or Middle I^udlow Rocks, 

 at Caynham Camp, near Ludlow. 



2. Mya mandibula. — The Jaw Mya, pi. XCII. fig. 13. 

 M. mandibula. Sowerby, I. p. 93, pi. 43. 

 Transversely elongated, its breadth being once and a half its 



length ; gibbose ; disk flattened in the middle ; anterior side 

 square, gaping, the opening oblong ; posterior side somewhat 

 straight; depth about two thirds its length ; surface with about 

 2.5 transverse undulations ; beaks pointed and incurved. 



Upper Greensand, Devizes anil Blackdown ; the Gault, 

 Isle of Wight and Dorsetshire ; and the Lower Greensand, 

 Pulborough and Lyme. 



3. Mya augiistata. — The Narrowed Mya, pi. XCII. figs. 

 26, 27, 28, 29. 



M. auffustata. Sowerby, "VI. p. 57, pi. 531, fig. 1. 



Transversely elongated ; its width sometimes thrice its 

 length ; valves unequal ; shell thin and antiquated ; irregularly 

 compressed ; both sides obtuse and gaping ; base of the lesser or 

 right valve concave ; beaks small, placed nearest the anterior 

 side. Hinge like those of M. sub-anffulata a,ad plana. 



The Upper Marl, Colwell Bay. 



i. Mya ovalis. — The Oval Mya, pi. XCII. figs. 24, 25. 



M. ovalis. Turton's Brit. Bia. pi. 3, fig. 1, 2. Alyapullus. 

 Sowerby, VI. p. 58, pi. 531, fig. 2. 



Transversely ovate ; its length a little more than half its 

 width ; anterior side longest and rounded ; posterior side 

 somewhat pointed ; surface concentrically striated, and a little 

 compressed ; lines of growth well defined. 



Mamraiferous Crag, Postwick ; the Red Crag, Butley, and 

 and the Pleistocene Marine Series, Isle of Bute. 



5. Mya arenaria.— The Sand Mya, pi. XCII. fig. 23. 



M. arenaria. Sowerby IV. p. 88, pi. 364. 



Transversely ovate ; anterior side pointed ; posterior side 

 rounded ; surface with concentrical sub-stiioe and undulations. 



The Pleistocene Marine Formation, Ayr and Dalrauir, Dum- 

 bartonshire ; the Mammiferous Crag, Bramerton, and Red 

 Crag, Sutton. 



6. Mya lata.— The Broad Mya, pi. XCIII. fig. 4. 

 M. lata. Sowerby, I. p. 185, pi. 81. 



Ovate ; length about two thirds its width, compressed ; an- 

 terior side acuminated and truncated, having an arcuated 

 margin, slightly gaping ; beaks rather produced and acute ; 

 surface smooth, with a few shallow undulations ; tooth very 

 large. 



The Mammiferous Crag, Bramerton, and the Red Crag, 

 Sutton. 



7. Mya ^quata.— The Equal Mya, pi. XCII. fig. 20. 

 M. cequata. Phillips, Geo. York, I. pi. 11, fig. 12. 

 Transversely oblong ovate ; beaks nearly central, and obtuse; 



sides equally rounded ; surface smooth. 



The Inferior Oolite, Blue Wick, Coldmoor. 



8. Mya calciformis. — The Shoe-Shaped Mya, pi. XCIII. 

 fig. 6. 



M. calciformis. Phillips, Geo. York, I. pi. 11, fig. 3. 



Transversely lengthened, short, rounded at both extremities ; 

 the posterior side a little narrowed ; a slight inflection towards 

 the centre at the base ; surface smooth. 



The Kelloways Rock, Scarborough, and the Inferior Oolite, 

 Blue \Vick, Cheltenham. 



9. Mya dilata.— The Dilated Mya, pi. XCII. fig. 18. 

 M. dilata. Phillips, Geo. York, I. pi. 11, fig. 4. 



Much elongated transversely, a little twisted ; anterior side 

 a little narrow at the extremity ; posterior side considerably 

 dilated and truncated, acute above and below ; beaks sub-cen- 

 tral, curved backwards, between which and the angle the bp,ck 

 is concave ; basal line nearly straight. 



The Inferior Oolite, Glaizedale. 



10. 51 ya L^viuscuLA. — Smooth Mya, pi. XCII. fig. 11. 

 M. Iwviiiscula. Sowerby, Geo. Tr. 2d Ser. IV, p. 340, 



pi. 16, fig. 6. 



Transversely oblong, somewhat square ; a depression from 

 the beaks to the base in the centre of the valves ; beaks rather 

 prominent ; sides bluntly rounded ; surface smooth, with a few 

 transverse wrinkles. 



The Greensand, Blackdown. 



11. Mya phasiolina. — The Little Pheasant Mya, pi. 

 XCII. fig. 21. 



M. phasiolina. Phillips, Geo. York, I. pi. 2, fig. 13. 

 An elongated ellipsis, both sides equally rounded ; beaks 

 obtuse ; surface smooth. 



The Speeton Clay, Specten, Yorkshire. 



12. Mya truncata.— The Truncated Mya, pi. XCIII. f. 1. 

 M. truncata. Brown, Illust. Rec. Conch. Brit., p. Ill, pi. 



45, fig. 2. 



Sub-ovate ; anterior side rounded ; posterior side much trun- 

 cated, and gaping widely ; hinge line nearly straight ; basal 

 line almost parallel to the back, and slightly hollow in the 

 middle ; surface with numerous concentric wrinkles. 



Pleistocene Marine Formation, Ayrshire, the Red Crag, 

 Sutton, and the Coral Crag, Ramshot. 



