492 DR WHE ELTON HIND ON 



Localities. — Mulloch Hill, Lower Llandovery ; Woodland Point, Middle Llandovery ; 

 and Penkhill, Upper Llandovery. 



Observations. — This species is much smaller and less gibbose than A. amygdalina, 

 from which it is probably descended. A single specimen only occurs in the Lower 

 and Middle Llandovery, but many examples were obtained from Penkhill. Fortunately, 

 one of these, fig. 6, PI. II., shows the posterior part of the hinge plate, and its generic 

 affinity is therefore certain. 



Genus Posidonomya, Bronn, 1837. 

 For synonymy, see Posidonomya, Hind, 1901, Brit. Carb. Lamell. (Pal. Soc), pt. ii. p. 26. 



Generic Characters. — Shell of moderate size, ovate, oblique, compressed, with an 

 anterior rounded ear and a compressed- expanded posterior ear. Hinge line straight ; 

 umbones small, pointed, placed anterior to the centre of the hinge line. Shell 

 obliquely but very moderately convex. 



Surface ornamented with numerous concentric grooves and ridges, occasionally 

 decussated by radiating lines. Periostracum well developed. 



Observations. — This genus is represented by five species in Carboniferous times, 

 and I have now referred to it a well-marked shell from the Middle Bala series. It 

 may be that, when details of the hinge plate turn up, a reconsideration of its 

 generic position may be necessary. 



Posidonomya antiqua, sp. nov. (PI. I., fig. \%.) 



Specific Characters. — Shell of medium size, moderately compressed, obliquely 

 U-shaped, inequilateral. The anterior border prolonged, very slightly convex. The 

 inferior margin strongly convex. The posterior border nearly straight and long. The 

 hinge line straight, making a well-marked, slightly obtuse angle with the posterior 

 border. The umbones are small, slightly raised, and placed far forwards. The valves 

 are obliquely gibbose, the postero-superior angle much compressed. 



Interior. — Unknown. 



Exterior. — The surface is ornamented by regular, raised, angular concentric ridges, 

 close in front, but becoming widely separated as they pass over the body of the valve. 

 The concave sulci which separate the ridges are finely striate concentrically. 



Dimensions. — -Difficult to estimate, on account of the imperfect state of the 

 specimen on which the species is founded, but the antero-posterior diameter was 

 probably 25-30 mm. The dorso-ventral diameter is at least 40 mm. 



Locality. — Middle Bala beds of Shalloch Mill. 



Observations. — M'Coy has described a somewhat similar shell from Ferriter's Cove, 

 Dingle, Co. Kerry (Silurian Fossils of Ireland, p. 22, pi. ii. fig. 10), as Pterinea (?) 

 posidoniaformis, but this species is figured as having its umbones subcentral, and 

 the anterior end is dissimilar to the species under description. The present specimen 



