128 



BRITISH SILURIAN BRACHIOPODA. 



there is a median longitudinal sulcus occupied by one or three smaller ribs. Surface of 

 valves closely and regularly crossed by concentric equidistant lines, and very minute 

 spinules cover the surface of the shell. Two specimens measured — 

 Length 8, width 7, depth 6 lines. 

 „ 6, „ 7, „ 4 

 Position and Locality. It is rare in the Wenlock limestone of Dudley ; more abun- 

 dant at Rock Farm, Longhope, whence very fine examples were prociu-ed by the late Rev. 

 J. Dyson, of Malvern. 



Retzia? Barraxdii, Davidson. PI. XIII, tigs. 10 — 13. 



Tekebratula Bakrandii, Dar. Bull. Soc. Geol. France, vol. v, 2ud ser., p. 332, pi. iii, 

 fig. 32, 1848. 



Rhynchonella — Salter. Siluria, 2nd edit., p. 250, Foss. 57, fig. 6, 1859. 

 Retzia — Id. lb., p. 544. 



— — Lindstrom. Gottlands Brach. ; Ofvers. K. Vet.-Akad. Forh., 



p. 337, 1860. 



Spec. Char. Shell small, almost circular, or slightly elongated oval ; ventral valve very 

 convex ; beak small, incurved, and truncated by a smaU foramen, partly margined by 

 a deltidium in two pieces ; surface ornamented with six large rounded ribs, of which 

 the two central are the most elevated, and are separated by a median concave sulcus. 

 Dorsal valve very slightly convex posteriorly, almost flat and even depressed in the 

 middle anteriorly ; lateral margins rounded and undulating, slightly truncated in front. 

 Surface ornamented by seven rounded ribs, of which the central one is on a little lower 

 level than those on either side. The valves are also regularly crossed by concentric lines 

 or ridges of growth. Interiorly spiral lamellae for the support of oral arms are attached 

 to the hinge-plate of the dorsal valve. Two specimens measured — 

 Length 4, width 4, depth 3 lines. 

 „ 3i, „ 3, „ 2 „ 

 Obs. This elegant little shell is easily distinguishable from other British Silurian 

 Brachiopoda. It has been considered by myself and others as one of the few Silmian forms 

 incertce sedis ; but recently some light has been thrown upon the subject by the discovery 

 made by Dr. Lindstrom and myself of portions of the spiral coils, which appear to agree in 

 position with those of Retzia. Dr. Carpenter has also at my request microscopically examined 

 the shell-structure, and writes — " The specimen of Retzia ? Barrandii which you enclosed 

 must have been stamped on in the Post-office ; for it came to me in powder. However, 

 this powder was very useful to me, for it enabled me to pick out a number of transparent 

 natural lamellae, the examination of which went to confirm what I had previously made by 

 sections from the specimens you had sent me some days before. The general texture of 

 the shell of R. Barrandii is rather Rhyiichonelline than Terebratuline, the two types being 



