ORTHIS. 165 



IV. Family — Strophomenidte, King, 1846. 



1. Genus — Orthis, Dalman, 1828. 



1. Orthis interlineata, Sowerby. Plate XX, figs. 6, 7. 



1810. Orthis interlineata, Sowerby. Geol. Trans., ser. 2, vol. v, pt. 3, pi. liii, 



fig. 11 ; and pi. liv, fig. 14. 



1840. — plicata, Sowerby. Ibid., pi. liii, fig. 10. 



1841. — interlineata, Phillips (pars). Pal. Foss., p. 63, pi. xxvi, figs. 



106 a, b (only). 

 1841. — parallela, Phillips. Ibid., p. 64, pi. xxvi, fig. 109 a — d. 



1865. — interlineata, Davidson. Brit. Foss. Bracb., vol. iii, p. 91, pi. xvii, 



figs. 18—23. 



Localities. — This shell is common and wide-spread. It occurs at Top 

 Orchard, Bradiford, Kingdon's Shirwell, Upcott, Braunton, Pilton, Wrafton 

 Lane, Saunton Point, Frankmarsh, Ashhill Quarry, Croyde, Petherwyn, and 

 Landlake. 



Size. — Height 12 mm., width 16 mm. 



Remarks. — The types of O. interlineata and O. plicata, Sowerby, which are in 

 the museum of the Geological Society, evidently belong to the same species. 

 Davidson also reunites with it Orthis parallela, Vh\]\ips, which Phillips had separated 

 from it. Orthis orbicularis, var., Murchison l (which Davidson seems to refer to in 

 his description of this species), does not seem distinguishable from it. Murchison, 

 himself, regarded his shell as distinct from the Orthis orbicularis 2 of the Silurian 

 System, which is united to O. lunata, Sowerby, 3 by Davidson. 



2. Orthis, sp. Plate XX, figs. 8, 8 a, 9. 



1841. Orthis interlineata, Phillips (pars). Pal. Foss., p. 63, pi. xxvi, figs. 



106 c, d (only). 

 ? 1841. — plicata, Phillips (not Sowerby) (pars). Ibid., p. 64, pi. xxvi, 



fig. 108 e (only). 



Description. — Shell minute, flat. Umbo elevated, prominent, rounded. Hinge- 

 line much shorter than the width of the shell. Lateral margins semicircular. 



1 1840, Murcbi3on, ' Bull. Soc. Geol. Fr.,' vol. xi, p. 255, pi. ii, figs. 8 a—c. 



2 1839, Sowerby, in Murchison, ' Sil. Syst.,' p. 611, pi. v, fig. 16. 



3 Ibid., p. 611, pi. v, fig. 15. 



