DE. T. DATIDSON ON RECENT BiJAClIIOPODA. 195 



of Orhictda striata. The same shell was also found some years ati^e by Mr. L. Binncy in 

 ballast-stone on the shores of the Clyde near Glasgow. 



It should also be recorded here that in a paper entitled " Observations on the Synonima 

 of the Genera Anomia, Crania, Orhicula, and Discina" published in the ' Annals of 

 Philosophy ' for 1825, Dr. J. E. Gray, of the British Museum, maintained that the genus 

 Discina -was established for the species under description. Both Mr. Dall and Mx. 

 Reeve have referred my Orhicula Bvunsi to Schumacher's or Lamarck's species, and 

 I am quite willing to agree to their identification. 



Subgenus Discinisca, Dall. 



107. Discinisca l^vis, Sowerby, sp. (Plate XXVI. figs. 1, 9-11.) 



Orhicula Icevis, Sowerby, Trans. Linn. Soc. vol. xiii. p. 468, pi. xxvi. fig. 1, a-d, (read in 1818) pub- 

 lished in 1822; G. B. Sowerby, Thes. Conch, i. p. 265, pi. Ixxiii. fi-s. 2, 3, 1846; Davidson, Ann. & 

 Mag. Nat. Hist. 2nd ser. vol. ix. p. 376, 1852. 



Discina Icevis, E. Suess, Ueber die Wohnsitze der Brachiopoden, Sitzungsb. k. Akad. "Wissensch. Wieu 

 Bd. xxxvii. p. 226, 1859. 



Orhicula Icevis, L. Reeve, Monogr. of Orhicula, Conch. Icon. pi. i. figs. 4 & 5, 1862. 



Discina Icevis, Dall, Amer. Journ. of Conch, vol. vii. p. 76, 1871 ; Bull. Mus. Comp. Zoiil. Harvard, 

 vol. iii. p. 42, 1871 ; and Proc. Acad. Nat. Sci. Philadephia, p. 201, 1873. 



Shell horny, almost orbicular, and nearly as wide as long, a little broader and more 

 rounded anteriorly. Surface either nearly smooth or more or less strongly marked with 

 concentric lines or ridges of growth. Upper valve compressed, limpet-like, or gently 

 conical. Vertex submarginal. Lower or smaller valve moderately convex, most 

 elevated towards the middle at about one third the length of the sliell from the posterior 

 margin. Central third of the posterior half of the valve abruptly depressed, with a 

 flattened, smooth, oval, or heart-shaped disk, wdiich does not quite reach the slightly 

 indented posterior margin of the shell. Along its centre an oval-shaped, narrow, 

 longitudinal fissure extends to within a short distance of the posterior ridge of the 

 disk, and through which a short stout peduncle passed, which expanded all over the disk 

 prior to becoming cylindrical, and again expanded at its extremity, where it became 

 firmly attached to some marine object. In the posterior half of the interior of the 

 larger valve a slightly sunken oblong depression occupies rather more than a third of the 

 breadth of the shell, and commences at some little distance from the posterior margin of 

 the valve. It is of an oblong shape, almost straight posteriorly, slightly indented 

 laterally and obtusely angular anteriorly. Along the posterior edge or portion are tw^o 

 transversely oval-shaped adductor scars, sejiarated by two other very small impressions 

 attributed to the retractor muscles ; on the anterior portion of the depressions or disk 

 are two larger obliquely placed adductor impressions, separated by a small rudimentary 

 ridge. In the interior of the smaller valve an elevated or convex disk occupies the 

 central third of the posterior half of the valve, and along the middle is a narrow oval- 

 shaped fissure, which extends along the disk to about half its length ; anteriorly a small 

 triangular-shaped septum divides the anterior pair of adductor muscles. Mantle highlv 

 vascular, fringed w^th setae, which extend to fully one third of the length of the shell 

 and beyond the margin of the shell. The labial appendages curve backwards, return 



