178 BRITISH CARBONIFEROUS BRACHIOPODA. 



are likewise more deeply longitudinally grooved than are others, while in the ventral valve 

 of certain examples there exists a median depression, which in others is converted into a 

 projecting ridge. 



It has appeared to me, after the attentive examination of about a dozen specimens, 

 that Prof, de Koninck's P. sub-lcevis and P. Ckristiani are only different conditions of a 

 same and single species, and should therefore be united. In England P. sub-lavis occurs 

 in the Carboniferous limestone of Clitheroe, in Lancashire, where it has been several times 

 obtained by Mr. J. Parker, Curator of the Manchester Museum. It has also been stated 

 to have been found in Wales, but no other British locality than that above given has 

 been correctly ascertained. On the Continent it has been found by M. de Koninck in the 

 Carboniferous limestone of Vise, in Belgium, and of Glageon, near Avesnes, in France, 

 and appears to have sometimes attained rather large dimensions, although nowhere hitherto 

 found in any profusion. 



Productus mesolobus, Phillips. PI. XXXI, figs. 6 — 9. 



Producta mesoloba, Phillips. Geol. of Yorks., vol. ii, pi. vii, figs. 12, 13, 1836. 

 Productus mesolobus, De Kon. Desc. des Anim. foss. du Terr. Carb. de Belgique, pi. xii, 



fig. 8, 1843; and Monograpliie du genre Productus, pi. xvii, 



fig. 2, 1847. 



— — De Verneuil. Russia and the Ural Mount., vol. ii, pi. xvi, fig. 8, 



1845. 



— — M'Coy. British Pal. Fossils, p. 468, 1855. 



— — Dav. Mon. of Scottish Carb. Brach., pi. xxi, 1861. 



Spec. Char. Shell thin, transversely oblong, and generally rather wider than long ; 

 hinge-line as long, and sometimes longer, than the average width of the shell ; ears or 

 cardinal extremities wide, and at times much extended. Ventral valve gibbous at the 

 beak, and somewhat geniculated towards the front, with a wide, flattened, or slightly con- 

 cave sinus, interrupted in the middle by a narrow median rib, and on either side of the 

 sinus a rib is present, while another intervenes between these and the cardinal angles. 

 The beak is proportionately large, and not overlying the hinge-line, except quite at its 

 attenuated extremity. Exteriorly the visceral disc is covered with numerous concentric 

 wrinkles, and a few tubular spines project from the five ribs. Dorsal valve concave, with 

 a narrow median groove and two slightly marked lateral ones, while the surface is covered 

 with concentric wrinkles and lines of growth. Interior unknown. Dimensions variable; 

 three British examples have measured — 



Length 11, width 19 lines. 

 9, „ 12 „ 

 „ 15, „ 14 „ 



Obs. Some foreign specimens have exceeded the proportions here given, and although 



