Lept^ina. 



MOLLUSCA. 



123 



12. Leptjena transvebsalis — The Transverse Leptaena, 

 pi. LIV. fig. 2, 3. 



Lepta'iia transversalis. Dalman, 1. c. p. 109, pi- 1, fig- 4. 

 lb. Hist. Pet. p. G9, pi. 20, fig. 5. Sowerby, Sil. Syst. p. 629, 

 pi. 13, fig. 2. 



Semicircular, greatly convex; lesser valve concave; hinge 

 inflected, with its line parallel, and equal to the width of the 

 shell; surface with wide-set, longitudinal ribs, and fine interme- 

 diate stria?. Length seven lines ; width somewhat more than 

 eight lines. 



Wenlock Shale, Tame Bridge and Hay Head, near Walsall; 

 Buildwas Bridge; Burrington; and Stumps Wood, near Led- 

 bury. 



13. LEPT.ENA MINIMA. — The Least Leptsena, pi. LIV. 

 fig. 6, 7. 



Leptana minima. Sowerby, Sil. Syst. p. 629, pi. 13, fig. 4. 



Semicircular ; hinge line parallel, very greatly inflated ; with 

 numerous, sharp, alternately long and short, smooth, radiating 

 ribs; sides a little prolonged, and auriform. Length two lines; 

 breadth three lines. 



Wenlock Shale, Burrington. 



14. Lept.ena l^vigata. — The Smooth Lepteena, pi. 

 LHL* fig. 35. 



Leptfena leevigata. Sowerby, Sil. Syst. p. 629, pi- 13, fig. 3. 



Semicircular, depressed ; hinge line parallel, its sides pro- 

 longed into short, auriform processes ; surface smooth, shining, 

 with a few radiating stria?, and small, obscure, concentric undu- 

 lations; base slightly depressed. Length two lines and a half; 

 width, exclusive of the prolonged sides, four lines. 



Wenlock Shale, Burrington, near Ludlovs-. 



15. Lept^na sericea. — The Silky Leptsena, pi. LHL* 

 fig. 23, 24. 



Leptana sericea. Sowerby, Sil. Syst. p. 636, pi. 19, fig- 1- 

 Leptana slriatella ? Dalman, 1. c. p. Ill, pi. 1, fig. 5. 



A transversely elongated semicircle ; larger valve convex, 

 the other much depressed, or nearly flat ; base considerably 

 deflected at the margin ; surface with a silky lustre, and very 

 numerous, close-set, radiating striae, a few of which are deeper 

 than the others ; some obscure, concentric lines of growth. 

 Length five lines ; breadth ten lines. 



Much resembling L. lata, but the strias are finer and more regular 

 sided, and the ba^^e more parallel. 



Lower Silurian Rocks at Whittingslow ; Horderley, Guils- 

 field, &c. 



16. Lept^na lata The Broad Lepfaena, pi. LIV. fig. 



19, 20. 



Leptcena lata. Von Buch. Sowerby, Sil. Syst. II. p. 603 

 and 610, pi. 3, fig. 10 b and 12 c, and pi. 5, fig. 13. Ure, Hist. 

 Ruth, and Kil. p. 317, pi. 16, fig. 10, II. 



Semicircular, with a rather straight base; upper valve convex, 

 slightly depressed in the middle; lower valve concave; covered 

 exteriorly with fine, radiating ridges; hinge line parallel, pro- 

 vided with from ciglit to ten tubular, simple, divaricating, thin, 

 tapering, acute spines. Length half its width. 



This is one of the most characteristic and abundant species of the 

 Upper Ludlow Rock. 



Found in the Old Red Sandstone at Felindre, Horeb Chapel; 

 in the Upper Ludlow Rock, Ludlow Promontory ; Dclbury ; 

 Munslow ; Woolhope Valley; Bagnor Hill; Presteign ; and 

 Lawrieston, near Rutherglen, Renfrewshire. 



17. LEPT.ENA COMPLANATA — The Even Lept<ena, pi. 

 LIV. fig. 12. 



Leptcena complanata. Sowerby, Sil. Syst. p. 636, pi. 20, 

 fig. 6. 



Semiovate, somewhat shorter than wide, much compressed ; 

 hinge line slightly arcuated, and rounded on both extremities; 

 beak a little produced ; surface with numerous, fine, radiating, 

 linear stria?, wliich increase in number towards the margin, 

 crossed towards the base by undulating lines of growth ; base 

 deflected. Length eleven lines ; width one inch. 



Lower Silurian Rocks at Acton Burncll, Shropshire. 



18. Lept^na duplicata — The Double-plaited Leptaena, 

 pi. LIV. fig. 13. 



LeptcBna duplicata. Sowerby, Sil. Syst. p. 636, pi. 22, fig. 2. 



Semicircular, transversely elongated, convex; inside of valves 

 with longitudinal furrows, arranged in pairs. Length five lines 

 and a half; width nine lines. 



Lower Silurian Rocks, Cefn, near Welshpool; and Robeston 

 Wathen, Pembrokeshire. 



19. Lept/Ena tenuistriata The Thin-striated Lep- 



tsna, pi. LIII.* fig. 12. 



LepAcena tenuistriata. Sowerby, Sil. Syst. p. 636, pi. 22, 

 fig. 2 a. 



Semicylindrical, with very numerous, close-set, longitudinal 

 stria3, crossed by from twelve to fourteen slight, concentric, 

 convex furrows ; sides expanded. 



Closely allied to L. depressa, but the striae are much finer and closer. 



Lower Silurian Rocks, Norbeth and Marloes Bay, Pembroke- 

 shire ; and in the Cardoc Limestone, Gaerfawr, Montgomery- 

 shire. 



20. Lept^na distorta The Distorted Lepta;na, pi. 



LIII.* fig. 2, 3, 4. 



Leptcena distorta. Sowerby, Min. Conch. VII, p. 10, pi. 

 615, fig. 3. 



Irregularly orbicular, convex ; hinge line parallel, with a tri- 

 angular area ; beaks prominent ; concentrically undulated, with 

 strong, longitudinal, interrupted stria; ; margins flattened. 



Distinguished from Z. analoga by its prominent beak, near to which 

 it is not compressed, and very convex valves. 



Carboniferous Limestone, Isle of Man. 



21. Leptaena ambigua. — The Ambiguous Leptjcna, pi. 

 LIV. fig. 16. 



Producta depressa. Phillips, Geo. York. II. p. 215, pi. 8, 

 fig. 18. 



Compressed ; hinge line nearly parallel ; beaks very slightly 

 produced; deeper valve concentrically angulated; whole surface 

 covered with rather strong, smooth, longitudinal, divergent 

 stria; ; crossed by flcxuous, rounded ribs, on the flat surface. 



Mountain Limestone, Florence Court. 



22. Lept^na plicatilis The Plicated Leptwna, pi. 



LIII.* fig. 6. 



Producta plicatilis. Sowerby, Min. Conch. V. p. 85, pi. 

 459, fig. 2. Phillips, Geo. York. H. p. 215, pi. 8, fig. 4. 



Transversely elongated; hinge line nearly parallel; umbo 

 slightly produced; a little hollow in the middle; surface with 

 transverse, prominent, somewhat flexuous, irregular ribs, and 

 fine, longitudinal, divergent stria;; basal line hollow in the 

 middle. 

 Mountain Limestone, Castlelon, Derbyshire. 



