Atrypa. 



MOLLUSCA. 



129 



Pentraedral; sides rounded; depressed; the mesial furrow in 

 both valves flattened ; surface covered with broad, undulating 

 fringes, the external or marginal one very greatly expanded. 



Mountain Limestone, Bolland. 



13. Atrypa fimbriata. — The Fringed Atrypa, pi. LIV. 

 fig. 72, 73. 



Atrypa Jimhriata. Sowerby, Min. Conch. VII. p. 16, pi. 

 617, fig. 4. Spirifera Jimhriata, Phillips, Geo. York. II. p. 

 220. See also p. 112. 



Transversely subovate, subcompressed ; centre of each valve 

 somewhat longitudinally depressed ; surface uneven, with im- 

 bricated and striated fringes. 



Mountain Limestone, Kendal, Westmorland. 



14. Atrypa protracta The Continued Atrypa, pi. 



LIV. fig. 55, 56. 



Atrypa protracta. Sowerby, Geo. Trans. V. 2nd series, pi. 

 56, fig. 16. 



Transverse, triangular ; lateral angles rounded ; beak pro- 

 duced, and acute ; sides flattened ; seam undulating ; base 

 elevated, with about four plaits, its sides smooth. 



Devonian Limestone, Plymouth. 



15. Atrypa oblonga. — The Oblong Atrypa, pi. LIV. 

 fig. 47, 48. 



Atrypa oblonga. Sowerby, Min. Conch. VII. p. 16, pi. 617, 

 fig. 3. 



Oblong-oval, very convex ; base hollowed ; beak small, 

 pointed, and incurved ; sides obtuse ; centre of each valve with 

 a plain, shallow, mesial furrow. 



There are some slight indications of its being fimbriated. 



Mountain Limestone, Queen's County, Ireland. 



16. Atrypa crenulata. — The Crenulated Atrypa, pi. 

 LIV. fig. 34, 35. 



Atrypa crenulata. Sowerby, Geo. Trans. V. 2nd series, pi. 

 56, fig. 17. Phillips, Pal. Fos. p. 85, pi. 34, fig. 152. 



Pentagonal, compressed ; surface smooth ; beak very small ; 

 base broadly and suddenly elevated ; with numerous, small, 

 lengthened crenulations near the margins ; sides smooth. 



Devonian Limestone, Barton and Plymouth, Devonshire. 



17. Atrypa pectinifera The Comb-like Atrypa, pi. 



LIV.» fig. 3, 4. 



Atrypa pectinifera. Sowerby, Min. Conch. VII. p. 14, pi. 

 616. 



Transversely obovate, equally convex, subcompressed ; beak 

 small ; surface covered with concentric, ciliated fringes ; the 

 external one with a rather lengthened fringe. 



Plentiful in the Magnesian Limestone, Humbleton Hill, near 

 Sunderland. 



18. Atrypa desquamata. — The Peeled Atrypa, pi. LVL* 

 fig. 1, 2, 3, 4. 



Atrypa desquamata. Sowerby, Geo. Trans. V. 2nd series, pi. 

 56, fig. 19, 20, 21, 22. Phillips, Pal. Fos. p. 82, pi. 33, fig. 146. 



Oblong, gibbous ; base obtuse, gently and broadly raised at 

 the edge, without elevating the surface ; smaller valve deeper 

 than the other; surface deeply striated longitudinally, increasing 

 in number towards the margin ; internal surface striated, or 

 punctated. 



This shell is liable to considerable variety in size, convexity, and 

 coarseness of striae. In the young condition specimens are found nearly 

 globular, while others are lenticular and compressed. 



Devonian Shales, Devonshire and Cornwall. 



A variety of this species is called by Sowerby Atrypa desqumata com- 

 pressa, fig. 21, 22. It is suborbicular, compressed, the valves equal, 

 with nearly rectangular sides. 



19. Atrypa fallax. — The False Atrypa, pi. LIV. fig. 18. 

 Atrypa fallax: Sowerby, Geo. Trans. V. 2nd series, pi. 54, 



fig. 15. Terebratula pleurodon, Phillips, Geo. York. II. p. 

 222, pi. 12, fig. 25, 26. 



Transversely ovate ; rather inflated, with many strong, ele- 

 vated, sharp ribs, and deep intervening furrows, producing a 

 strongly crenulated margin. 



Devonian Shale at Petherwin and Barnstaple. 



20. Atrypa hispida The Bristly Atrypa, pi. LIV. fig. 1. 



Atrypa hispida. Sowerby, Geo. Trans. V. 2nd series, pi. 



54, fig. 4. 



Transversely oval, compressed ; beak but slightly produced ; 

 surface with concentric fringes of spines. 



Devonian Limestone, Petherwin. 



21. Atrypa impleta. — The Filled-up Atrypa, pi. LIV. 

 fig. 32, 33. 



Atrypa impleta. Sowerby, Geo. Trans. V. 2nd series, pi. 

 57, fig. 2. 



Transversely elongated, its width considerably more than its 

 length, ventricose ; sides rounded ; beaks slightly produced ; 

 base elevated, with six furrows ; whole surface with radiating 

 flattened ribs and shallow furrows. 



Devonian Limestone at Plymouth. 



22. Atrypa implexa. — The Plaited Atrypa, pi. LIV. fig. 

 83, 84. 



Atrypa implexa. Sowerby, Geo. Trans. V. 2nd series, pi. 

 57, fig. 4. 



Transversely obovate; base straight, flat; margin of the base 

 and sides broad; surface with numerous, acute plaits, producing 

 a toothed margin, with the edges of the valves deeply locked 

 into each other. 



Devonian Limestone, Plymouth. 



23. Atrypa triloba. — The Three-lobed Atrypa, pi. LIV. 

 fig. 27. 



Atrypa triloba. Sowerby, Geo. Trans. V. 2nd series, pi. 

 56, fig. 14. 



Tetrahedral, with rounded angles, three lobed ; upper valve 

 much inflated; lower one nearly flat; base much elevated, with 

 about twelve plaits, its sides smooth; lateral lobes reflexed, and 

 obscurely plaited ; whole surface with broad, flat, radiating ribs, 

 and shallow intervening furrows. 



Devonian Limestone, Plymouth. 



24. Atrypa triangularis The Triangular Atrypa, pi. 



LIV.* fig. 9. 



Atrypa triangularis. Sowerby, Geo. Trans. V. 2nd series, 

 pi. 54, fig. 9. 



Triangular; base with two folds; beaks hardly produced 

 beyond the circumference of the valves. 



Ferruginous Soft Devonian Limestone, Plymouth. 



25. Atbypa subdentata. — The Half-toothed Atrypa, pi. 

 LIV. fig. 36, 37. 



Atrypa subdentata. Sowerby, Geo. Trans. V. 2nd series, 

 pi. 54, fig. 7. Terebratula subdentata, Phillips, Pal. Fos. p. 

 90, pi. 35, fig. 164. Terebratula rotunda, Miinster, Beit. 3, 

 pi. 14, fig. 15. 



Orbicular, somewhat longer than wide, a little convex, smooth ; 

 beak very small, but prominent ; base three-plaited, and raised. 

 2k 



