THE LAMELLIBRANCHS OF THE SILURIAN ROCKS OF GIRVAN. 527 



Locality. — Woodland Point, Middle Llandovery. 



Observations. — I have referred this shell provisionally to Palseoneilo, on account of 

 the deep and well-marked escutcheon and the smooth surface. If I am right, this 

 species differs from many others in having no fold posteriorly below the dorsal slope. 

 The general shape of the shell is more like Ctenodonta ; but the latter has no 

 escutcheon. Nuculana has an escutcheon ; but as far as I know the shell is always 

 marked with fine but definite regular concentric lines. The material at my disposal is 

 a single left valve, and it is to be hoped that more specimens may be obtained with a 

 view of the hinge plate, that the true generic affinity of the species may be settled. 



Palseoneilo sinuatus, sp. nov. (PI. III., figs. 26, 27.) 



Specific Characters. — Shell below medium size, transversely subquadrate, obliquely 

 gibbose, with a well-marked oblique sinus, reaching from the umbo to the lower margin, 

 marking off a very small anterior end from the rest of the valve. Posterior superior 

 angle compressed. The anterior margin short, rounded, the inferior gently sinuous, the 

 posterior broad and bluntly convex. The hinge line straight behind, arched and 

 depressed in front. The umbones are compressed, obtuse, and projecting over the 

 small anterior end, which they overshadow, terminal. 



Interior. — -Not exposed. 



Exterior. —The surface is ornamented with close, raised, concentric lines and rugae 

 of growth. 



Dimensions. — Fig. 26, PI. III., a right valve, measures : antero-posteriorly, 20 mm. ; 

 dorso-ventrally, 13 mm. 



Localities. — Middle Llandovery of Woodland Point ; Middle Bala of Whitehaven 

 Bay and Shalloch Mill. 



Observations. — I doubtfully refer this species to Palseoneilo, chiefly on account of 

 the sinuate form of its posterior end. Unfortunately, no details of the interior are 

 exposed. Six specimens are in the Gray Collection, four of which are labelled 

 "Woodland Point." 



Genus Clidophorus, Hall, 1847. 



Cucull&a, Sowerby, 1839, Silurian Syst., pt. ii. p. 602, pi. iii. figs. 16, 12a, b. 

 Clidophorus, Hall, 1847, Pal. New York, vol. i. p. 300. 



M'Coy, 1855, Brit. Pal. Foss., p. 273. 



Miller, 1889, North Amer. Geol. and Pal., p. 471. 

 „ Ulrich, 1897, Geol. Minnesota, vol. iii., pt. ii., Pal., p. 606. 



Generic Characters. — Shell transverse, compressed, oblong, obliquely gibbose, 

 equivalve, inequilateral. Umbones small in the anterior third of the valve. 

 Apparently no lunule or escutcheon. 



Interior. — Hinge edentulous ; a vertical process passes downwards from the hinge 

 TRANS. ROY. SOC. EDIN., VOL. XLVII. PART III. (NO. 18). 77 



