494 DR WHEELTON HIND ON 



Pterinea elegans, sp. nov. (PI. I. fig. 6.) 



Specific Characters. — Shell subquadrate, U-shaped, moderately gibbose. The 

 anterior end is compressed and short, its border sinuous, the inferior border expanded 

 and bluntly rounded, the posterior almost straight, only very slightly concave above. 

 The hinge line is straight, slightly produced, making a small acute angle with the 

 posterior border. The umbo is small, placed in front of the middle joint of the hinge 

 line, slightly elevated and incurved. The anterior lobe is small, the posterior superior 

 angle compressed and subalate. 



Interior. — Not seen. 



Exterior. — The surface is very beautifully marked with regular, well-marked and 

 sharp concentric lines, which follow the contour of the valve. Towards the lower 

 and posterior part a few broad, very shallow radiating flexuous ribs are to be seen. 



Dimensions. — Fig. 6, PI. I., measures: antero-posteriorly, 15 mm.; dorso-ventrally, 

 20 mm. ; elevation of valve, 3 mm. 



Locality. — Craigens Quarry, Lower Llandovery. 



Observations. — I have erected this species on a single specimen, consisting of two 

 portions, the cast and its mould. The beautiful external ornament is preserved in the 

 latter, and can be studied by moulds of modelling wax. The specimen is a left valve. 

 It is more quadrate and has a shorter hinge line, and the posterior border is not so 

 falcate as in the other Silurian species, none of which possess the characteristic ornament 

 which I have described. 



Pterinea reticulata, sp. nov. (PI. I. figs. 7, 8.) 



Specific Characters. — Shell small. Body of the valve ovate acute, swollen ; 

 anterior end comparatively large, auriculate, rolled. The posterior subalate, com- 

 pressed. The anterior margin sinuous, the inferior rounded, the posterior rounded 

 below, falcate above. The hinge line straight, produced. The umbone small, pointed, 

 incurved, subcentral. The convex body of the valve is marked off from the anterior 

 end by an oblique shallow sinus. 



Interior. — Hinge plate and muscle scars normal. 



Exterior. — The body of the valve is ornamented by radiating ribs somewhat sharp 

 and flexuous, crossed by fine raised concentric lines, so that the surface is markedly 

 reticulate. The anterior radiating ribs are absent, and the lines of growth are so 

 strong as to be subimbricate. Apparently the radiating ribs are also obsolete on the 

 posterior wing. 



Measurements.— Fig. 1, PL L, a left valve, incomplete posteriorly, measures: 

 antero-posteriorly, 15 mm. (circ.) ; dorso-ventrally, 12 mm. 



Locality. — The Star-fish bed, Upper Bala. 



Observations. — This shell has well-marked characters and can be easily recognised. 



