ORDOVICIAN AND SILURIAN BRACHIOPODA OF THE OxIRVAN DISTRICT. 801 



and traces of paired muscle-scars. Brachial valve slightly concave ; with short 

 oroove across posterior thickened margin ; muscle-scars indistinct. 



Dimensions. — Diameter of shell, 3-4 mm. 



Horizon. — Whitehouse Group. 



Localities. — Whitehouse Bay, Shalloch Mill. 



Remarks. — This small shell much resembles Paterula balclatchiensis in its 

 general character and thickened margin, but we may entertain some doubt as to 

 its right generic position. Traces of a pair of small subcentral scars and a shield- 

 shaped muscle-area are visible in some pedicle-valves. It seems, however, distinct 

 from Pholidops antiqua, which is found on the same horizon. 



Paterula ? Jamesoni, sp. nov. 

 (Plate I, figs. 26-28.) 



1883. Discina 1 balcletchiensis, Davidson (pars), Mori. Brit. Foss. Brach., vol. v, Silur. Suj>pl., p. 210, 

 pi. xvii, figs. 42, 42a (non fig. 41). 



Shell subcircular to oval, rather longer than wide, both valves gently convex, 

 low ; apex very excentric, situated close to posterior margin, gently raised, with 

 short steep posterior slope. Interior of brachial (?) valve with narrow flattened 

 regular smooth limb, and two pairs of small subcircular muscle-scars, of which the 

 posterior pair is situated at about one-fourth the length of shell and are larger than 

 the anterior pair, which are closer together and subcentral ; a faint narrow elongated 

 scar divided by a fine median line is situated just in front of the anterior pair of 

 scars ; behind the pair of posterior scars is a fine wavy impressed transverse line, 

 thickened in middle ; traces of fine faint radial lines are seen running forwards from 

 the posterior scars. External surface of valve ornamented with fine concentric striae. 



Dimensions. — Length, 2'8 mm. ; width, 2'5 mm. 



Horizon. — Drummuck Group (Starfish Bed). 



Locality. — Thraive Glen. 



Remarks. — The true generic position of this little shell is doubtful. The general 

 appearance recalls Paterula oalclatchiensis , but the margin is apparently entire. 

 There is no scutellum as in Pholidops, which otherwise it resembles. The muscle - 

 scars are somewhat like Pseudocrania, but the transverse impressed posterior line 

 suggests the " crescent" of the Trimerelloids. 



The specific name is given in honour of the Scotch geologist Robert Jameson. 



Genus Dinoboltjs, Hall. 



Dinobolus Davidsoni (Salter). 



1853. Obolus Davidsoni, Salter MS., Davidson, Mori. Brit. Foss. Brach., vol. i, p. 136, figs. 54-56. 

 1866. Obolus Davidsoni, Salter, Davidson, op. cit, vol. iii, pt. vii, p. 58, pi. iv, figs. 30-39. 



