168 



BRITISH SILURIAN BRACHIOPODA. 



Rhynchonella Wilsoni, Bav. Annals and Mag. of Nat. Hist., 2nd ser., vol. u, 

 pi. xiii, 1852. 



Hemithtuis — M'Coy. Brit. Pal. Foss., p. 207, 1852. 

 Rhynchonella — Morris. Catal. of British Fossils, p. 148, 1854. 

 Anomia lacunosa, Hanley. Ipsa Linnaei Conchylia, p. 128, 1855. 

 Rhynchonella Wilsonl, Schmidt. Archiv Nat. Liv.- Ehst.- und Kurlands, vol. ii, 

 p. 210, 1858. 



— D' Eichwald. Lethsea Rossica, vol. i, p. 762, 1859. 



— — Salter. Siluria, 2nd ed., p. 545, pi. xxii, fig. 13, 1859. 



— PENTAGONA, Id. lb., p. 545, pi. xxii, fig. 3, 1859. 



— CREBRicosTA, Id. lb., p. 544, pi. xxii, fig. 3, 1859. 



— Wilsoni, Lindstrdm. Gottland Brach., p. 366, 1860. 



— — Salter. Explan. Sheets 160, &c., Geol. Survey Ireland, 



p. 13, 1863. 



I 



Spec. Char. Subpentagonal, but generally cubical, and often sub -spherical, about as 

 wide as long ; sides and front rounded ; valves almost equally gibbous, and often so 

 much so that the shell is twice as deep as either long or wide, and presents, when 

 viewed in front or in profile, an elongated oval shape. Dorsal valve somewhat flattened, 

 or gently convex at the umbone, with a slight longitudinal depression or groove along its 

 middle ; in front abruptly deflected, and almost perpendicular before meeting the margin 

 of the opposite valve; fold wide, nearly flat, and in the ordinary varieties not raised 

 above the general convexity of the valve. Ventral valve flattened or slightly convex 

 posteriorly, but in front abruptly deflected, and becoming almost perpendicular as it meets 

 the acutely dentated margin of the dorsal valve; sinus wide, oblong, square, and nearly fiat, 

 very shallow, and scarcely defined on the surface ; beak small, much incurved, and usually 

 so much appressed to the umbone of the dorsal valve that no foramen is visible ; beak- 

 ridges strongly marked, leaving a concave space between them and the hinge-line. Surface 

 of both valves ornamented with from thirty to forty small, usually simple ribs, of which 

 from six to nine occupy the fold and sinus ; the ribs are likewise usually divided or 

 indented along the middle in their proximity to the serrated margin. On the inner 

 surface of the dorsal valve, under the divided hinge-plate, is a mesial ridge of small 

 elevation, which extends less than half the length of the valve, and divides the slightly 

 marked muscular impressions. In the ventral valve a depressed median scar, longi- 

 tudinal and oval, is surrounded by a large saucer-shaped muscular impression. Two 

 large specimens measured — 



Length 13, width 13, depth lli lines. 



7 „ 7 „ 10 „ but the shell is usually smaller. 



Obs. As this important Upper Silurian species has by some authors been referred 

 to Linne's Anomia lacunosa, it will be desirable to search its history. In the 

 twelfth edition of the 'Systema Naturae,' p. 1153, 1767, Linne describes his Anomia 

 lacunosa as follows : — " A. testa subrotunda multisulcata ; valvulis apice plicatis ; altera 



