Mya. MOLLUSCA. MYAD^. 463 



Length about 2 inches, breadth 3 inches ; white, with a thin cuticle often 

 of rusty colour ; coucentricall)'^ striated ; smooth in the middle ; the broad 

 vertical tooth has usually an oblique rib from the beak to its retra| angle, and 

 is marginated anteally ; the j)it in the opposite valve for the ligament is hori- 

 zontal, with a small tooth or projection on its an teal margin. The animal 

 is frequently used as food, when boiled- In Zetland it is so used, and is call- 

 ed Smurslin. 



577. M. urenar'ia. — Shell rounded at both extremities ; the 



retral one slightly produced and attenuated. 



Linn. Syst. i. 1112. Penn. Brit. Zool. iv. 79- t. xlii. Mont. Test. Brit. 

 30. Turt. Biv. Brit. 32. — Common near low water-mark, lodged in 

 sand or gravel. 



Length sometimes reaching 3 inches, breadth five and a half; it chiefly dif- 

 fers from the last in the production of the posterior extremity, by the presence 

 of a few obsolete longitudinal ridges, in bemg more compressed, and the tooth 

 rounder, syphon impression more conical — This species, called at Southamp- 

 ton Old Maids^ and at Cork Sugar Loons., is more frequently found in estuaries 

 under the influence of fresh water, than the preceding. The 31. ovalisot"Dv 

 Turton, Biv. Brit. 33. t. iii. f. 1, 2, seems nothing more than the young of M. 

 arenaria, " with the tooth flattened at the top, and flexuous." 



578. M. Noncegica. — Dorsal margin nearly straight, waved 

 and truncated retrally, rounded anteally. 



Turt. Linn.'iv. 178 — M. striata, Mont. Linn. Trans, xi. 188. t. xiii. f. 1. 



— M. pellucida. Brown, Wern. Mem. ii. 505. t. xxiv. f. 1 Lyonsia 



striata, Turt. Biv. Brit. 35. t. iii. f. 6, 7 — English and Irish coasts. 

 Length half an inch, breadth an inch ; thm, semitransparent, with a brown 

 cuticle, rugged retrall}^ ; longitudinally striated ; inequivalve. According to 

 Dr Turton (whom I have followed in bringing together the preceding syno- 

 nims, not, however, without considerable hesitation), the tooth is an indepen- 

 dent process, moveable with the ligament. 



579- M. decussata. — Ovate, with irregular concentric ridges, 

 decussated by regular longitudinal striae. 



Mont. Test. Brit. Sup. 20 — Frith of Forth, Afr Laskey. 



Diameter about half an inch ; white ; margin waved ; umbo-obtuse, re- 

 curved, and placed nearest to one end ; a tongue-shaped syphon mark ; in one 

 valve a broad erect tooth, in the other a projecting plate, with a small inden- 

 ture for the reception of the tooth of the opposite valve. Its generic relations 

 uncertain. 



EXTINCT SPECIES. 



1. M. mandibnla. — Gibbose, flattish in the middle, transversely undulated ; 

 retral side square, gaping, anteally straightish — Smoer. Min. Conch, t. xliii. 

 In Green Sand. 



2. M. intermedia. — Depressed, smooth, twice as wide as long ; sides round- 

 ed, the anteal one small, the retral one expanded and gaping a little.— i^ower. 

 Min, Conch, t. Ixxvi. f. 1, and t. ccccxix. f. 2. — London Clay. 



3. M. jofejia.— Rather depressed, smooth ; wider than long ; ovate ; nearU 

 equilateral ; retral side rather elongated— iJowen Min. Conch, t. Ixxvi. f. 2,-1- 

 Plastic Clay. 



