NUCULA LiEVIROSTRUM. 183 



Nucula l^evirostrum, Portlock, 1843. Plate XV, figs. 32, 34—38, 38 a. 



NtrctTLA L.2EVIEOSTEUM, Portlock, 1843. Eeport Geology Londonderry, p. 439, 



pi. xxxvi, fig. 12. 



— longieosteis, M'Coy, 1845. Carbonif. Fossils Ireland, p. 70, pi. xi, 



fig. 19 (figure, not description). 



— clavata, M'Coy, 1845. Carbonif. Fossils Ireland, p. 69 (description, not 



figure). 



— longieosteis, Brown, 1849. Fossil Conchology, p. 189. 



— l^vieosteis, Brown. Ibid, (not figured). 



Leda longieosteis, d'Orbigny, 1850. Prodrome Paleont., p. 130. 

 Ctenodonta, sp. ?, Salter, 1864. Geol. Country round Oldham, p. 65, pi. i, fig. 3. 

 Nuccla caebonaeia, Eichivald, 1860. Lethaea Rossica, p. 994, pi. xxxviii, fig. 12. 

 Leda longieosteis, Youny and Armstrong, 1871. Trans. Geol. Soc. Glasgow, 



vol. iii, Appendix, p. 52. 

 Nucula l^vieostrum, Young and Armstrong, 1871. Ibid., p. 53. 

 Ctenodonta l^tieosteum, Bigsby, 1875. Thesaur. Devonio-Carboniferus, p. 303. 

 Ntjcula l^vieosteis, Etheridge, 1885. Brit. Foss., part 1, Palteoz., p. 287. 



— longieosteis, Etheridge, 1885. Ibidem. 



Specific Characters. — Shell moderately convex, transversely navicular. The 

 anterior end is well developed, and has a rounded border, which descends in a 

 regular curve to about the centre of the inferior border. The latter is very convex, 

 the posterior portion curving upwards, and more nearly straight. The posterior 

 end is produced, compressed, greatly narrowed, with a blunt, short border, more or 

 less acutely pointed, considerably nearer the upper than the lower margin. The 

 hinge-line is arcuate ; anterior portion shorter than the posterior. The umbones 

 are small, tumid, incurved, twisted forwards, situated at the junction of the 

 anterior and middle thirds of the shell ; contiguous and excavated in front by a 

 cordate lunule. The valves are evenly convex, the greatest convexity being at 

 the centre. Passing downwards from the posterior edge of the umbo is a very 

 obscure ridge, often obsolete, which is directed downwards and backwards to the 

 lower border of the shell, just anterior to the posterior-inferior angle. There 

 is no escutcheon or lunule. The shell is very thin. 



Interior. — The adductor scars are extremely shallow and inconspicuous. The 

 anterior is situated at the upper margin, just in front of and below the umbo, and 

 separated from it by a groove. The posterior is high up, and within the posterior 

 slope of the shell. The hinge is multidenticulate, and consists of two portions, 

 an anterior and a posterior, which are slightly inclined to each other at a very 



