Unio. 



CONCHIFERA. 



179 



Pachi/odon transtersus. Brown, Ann. Nat. Hist. Dec. 

 iS4.:3, pi. 1(),* fig. 5. 



Transversely elongated ; uinbonos blunt and obliquely 

 rounded ; anterior side short, rounded, and slightly produced at 

 the extremity ; posterior side long, gradually declining from 

 the umboncs, ending in an obliquely truncate termination, 

 rather acutely beaked below ; hingo-line nearly straight, basal 

 liue with a slight flexure posteriorly ; surface rather smooth. 



Coal Shale at Middlcton, near Leeds. 



2+. Unio iumatus. — The Buried Uuio, pi. LXXII. f. 18. 



Pachyodon /iumatus. Brown, Ann. Nat. Hist. Dec. 1843, 

 pi. 16,* fig. G. 



Oblong-ovate, considerably inflated ; umboncs large, pro- 

 duced, and slightly inflected; anterior side rounded, posterior 

 side sub-acute ; hinge-line nearly parallel ; basal margin a little 

 arcuated ; surface with strong concentric wrinkles. 



In the Coal Shale at Gristhorpe Bay. 



25. Unio levedexsis. — The Coarse Unio, pl.LXXIII.f.30. 



Pachyodon lecedensis. Brown, Ann. Nat. Hist. Dec. 1843, 

 pi. IG,* fig. 8. 



Sub-triangular, wedge-shaped ; umboncs rounded, situate 

 considerably to one side ; anterior side very short and abruptly 

 descending ; jiosterior side long, acuminated, its superior 

 margin gnulually inclining to a truncated termination ; basal 

 margin nearly straight ; surface with transverse antiquated 

 wrinkles. 



Coal Shale at Middleton. 

 2G. Unio pyhamid.\mj.s. — The Pyramidal Unio, pi. 

 LXXni. f. 19. 



Pachyodon fyramxdalus. Brown, Ann. Nat. Hist. Dec. 

 1843, pi. Ifi,* fig. 9. 



Sub-triangular, cuneiform, somewhat pyramidal ; umboncs 

 large, contiguous, extremely obtuse ; anterior side very short, 

 abruptly descending and rounded below ; posterior side elon- 

 gated, its superior line gradually descending to a blent acumi- 

 nated termination, thick oi; the anterior side, and becoming 

 ra])idly compressed posteriorly ; base acute, slightly flexuoso 

 and thin at the edge; surface with shallow irregular wrinkles ; 

 thickness equal to two-tliirds its length. 



Ironstone Shale at Low Aioore ; also in Shale at TVoodhall, 

 near Edinburgh. 



27. Unio Alda.mii. — Aldam's Unio, pi. LXXIIl. fig. 18. 



Pachyftdon Aldamu. Brown, Ann. Nat. Hist. Dec. 1843, 

 pi. 16,»"fig. 3. 



Sub-compressed, fleiQose, and sub-triangular ; umboues sub- 

 central, very obtuse, set one-eighth of an inch apart ; hinge- 

 line slightly arcuated ; anterior side abruptly descending from 

 the umboncs, beneath which it is slightly rounded, with a 

 flexure below, somewhat produced on the margin immediately 

 under the umbones ; posterior side gently sloping and rounded, 

 with a shallow furrow emanating from below the umbones, 

 and rapidly widening, terminates on the ba.=!c ; ba.sal lino 

 flexuose. Length one inch five-eighths ; breadth two inches 

 one-eighth ; thickness one inch. 



The greatest thickness of the shell is at the middle of the 

 disk, from whence it rapidly becomes thin towards the 

 margins. 



Coal Shale at Whitehaven. 



Named in honour of Miss Aldam of Leeds, an excellent conchologist. 



28. Unio cordiformis. — The Heart-shaped Unio, pi. 

 LXIV. fig 21. 



U. cordiformis. Sowerby, VI. p. 191, pi. 59.5, fig. 1. 



Heart-shaped ; posterior side rounded ; anterior side pointed, 

 its length and thickness being nearly equal ; beaks rounded, 

 large, and considerably produced. 



The Weald Clay, Tilgate Forest. 



29. Unio shb-truncatus — The Sub-truncated Unio, pi. 

 LXXIV. fig. 6. 



U. suh-truncattts. Sowerby, Geo. Trans. 2d Ser. IV. p. 

 346, pi. 21, fig. 15. 



Ovate, compressed ; edges of the valves obtuse ; posterior 

 side obliquely wedge-shaped ; beaks small and a little remote. 



The Hastings Sand, Sussex. 



30. Unio Martini. — Martin's Unio, pi. LXXIV. fig. 7. 

 U. Martini. Sowerby, Geo. Tr. 2d. Ser. IV. p. 346, pi. 



21, fig. 7. 



Convex, beaks slightly produced and nearly central : poste- 

 rior side very large and rounded ; anterior side somewhat 

 acute ; surface nearly smooth. 



The Weald Clay, Henhurst, Sussex. 



31. Unio Maxtellii.— Mantell's Unio, pi. LXXIV. 

 fig. 16. 



U. Mantellii. Sowerby, Geo. Tr. 2d Ser. IV. p. 346, pi. 

 21, fig. 14. 



Oblong-ovate, compressed, with the dorsal and basal margins 

 nearly parallel and straight ; posterior side short ; anterior 

 side lengthened ; beaks slightly produced ; surface smooth ; 

 length about equil to half the breadth. 



The Weald Clay and Hastings Sand, Sussex. 



32. Unio tdmidus.— The Swollen Unio, pi. LXXIV.* 

 figs. 5, 6. 



U. tumidus. Brown, Illust. Land and Fresh-water Shells, 

 p. 110, pi. 21, figs. 8, 9. 



Somewhat cylindrical, or wedge-shaped ; much inflated, 

 with the beaks produced ; anterior side short, rounded ; poste- 

 rior side long, gradually sloping from the beaks ; the termina- 

 tion sub-truncated ; cardinal tooth large, thick, and elevated, 

 with the edge finely serrated, and double in the opposite valve ; 

 muscular impressions small ; surface with strong concentric, 

 wrinkles. 



The Pleistocene Fresh-water Formation, Sutton, Grays, and 

 Cropthorn. 



33. Unio ovalis.— The Oval Unio.pl. LXXIV.* f. 3, 4. 

 U. ovalis. Brown, Land and Frosh-watcr Shells, p. Ill, 



pi. IS, figs. 4, 5. 



Transversely ovate ; hinge-liue arcuated ; beaks prominent, 

 wrinkled, and closely approximate; right valve with a strong 

 double, erect, cardinal tooth, the higher portion situate below 

 the beak, and considerably elevated above the margin, with 

 two long, obli(jue, lateral teeth; muscular imj)ressions of mo- 

 derate size, the anterior ones deep ; left valve with a simple, 

 erect, oblique, cardinal tooth, and a long, elevated, lateral one 

 which fits into the cleft between those of the opposite valve. 



The Pleistocene Formation, Cropthorn. 



34. Unio Solanuki. — Solander's Unio, jd. LXXIV. f. 10. 

 U. Solundri. Sowerby, Min. Conch. VI. p. 29, pi. 517, 



Fleming, Brit. An. p. 417. 



Shell transversely oblong-ovate, compressed, thin ; hinge- 



