R. Etheridge,jun. — New Carboniferous Mollusca. 305 



8p. chars. — Variable in outline, but generally irregularly ovate, 

 compressed, occasionally assuming an oblique form, at times narrowed 

 towards the beaks, and expanded towards the ventral margin ; beaks, 

 in the ovate forms nearly central, in the oblique forms nearer the 

 anterior end, sharp, prominent ; anterior end rounded ; posterior end 

 somewhat truncated ; the distinguishing character of the shell is the 

 very irregular concentric wrinkles which cover the surface ; in nearly 

 all adult specimens these are supplemented by a variable number of 

 strongly wrinkled ribs, which radiate from the beak to the ventral 

 margin on the centre of the shell only, leaving the anterior and pos- 

 terior ends merely covered with the concentric markings ; shell thin. 



Obs. — This shell was originally regarded as a species of Anomia, 

 but the examination of a large series of specimens, many showing 

 both valves united, has convinced me that it has nearer affinities 

 with Posidonomya. Not a single specimen has shown the perforated 

 valve of Anomia. Posidonomya Gibsoni, Brown, ^ is a closely allied 

 shell, and is equally variable and coarsely wrinkled, but wants the 

 radiating ribs. In the possession of the latter, P. corrugata ap- 

 proaches McCoy's P. costata,- but has in addition the concentric 

 wrinkles, which are absent in the Irish shell. In this species the 

 radiating ribs are confined to the number four in each individual, 

 whilst in P. corrugata they are variable, as few as two and as 

 many as seven have been noted. Highly gregarious, and at certain 

 localities very common. 



Locality and Position. — North Lickprivick Farm Old Quarry, near 

 E. Kilbride, Lanarkshire, in shale above the Main Limestone ; 

 Fiddler's burn, opposite Headsmuir, near Carluke, Lanarkshire, in . 

 shale below Eaesgill Ironstone ; Jock's burn above Hallcraig Bridge, 

 near Carluke, in shale between the First Kingshaw Limestone and the 

 Lingula Limestone, and also in the latter ; Burnbrae Old Quarry, Gill 

 burn. Quarry near Mossneuk Farm House, and burn under Burn- 

 head Farm House, all near E. Kilbride, in shale immediately below 

 Calderwood Cement Stone ; Old Quarry, near Limekilns House, 

 near E. Kilbride, in the Calderwood Cement Stone ; Kirktonholm 

 Cement Works, Calderside Cement Works, Boghead Quarry, and 

 Newfield Farm Cement Works, all near E. Kilbride, in shale above 

 Calderwood Cement Stone (Geol. Survey of Scotland).^ 



EXPLANATION OF PLATE XIII. 

 Fig. 1. — Peeten Sowerbii, McCoy. Showing the conate ears and V-strise. Slightly 



enlarged. L. Limestone series. Esperston, near Edinburgh. 

 Fig. 2. — Another specimen, much compressed, with the ears wanting. 



and in the other forming, at the beaks, a retreating angle (Illinois Geol. Rep. iii. 

 page 454). It may be that the two valves of P. Sowerbii differed in a somewhat 

 analogous manner ; this, however, is a point which can only be proved by those pos- 

 sessing specimens showing the valves in union. Messrs. Meek and "Worthen point 

 out the resemblance of P. Shumardianiis to P. Sowerbii. 



1 Salter, Mems. Geol. Survey England and Wales, Country around "Wigan, 1862, 

 p. 35, fig. 1, b. 



2 Synop. Carb. Eos. 1844, p. 78, t. 13, fig. 15. 



3 Recorded as Anomia corrugata by Messrs. Armstrong and Young, from Boghead, 

 in a thin band of Limestone, in the Upper Black Shale, and Dalrey, Ayrshire, iu the 

 Lower Limestone. (Trans. Geol. Soc. Glasgow, iii. app. p. 45.) 



DECADE II. — VOL. I. NO. VU. 20 



