CARBONICOLA NUCULARIS. 63 



8. Carbonicola nucularis, sp. nov. Plate VII, figs. 24 — 42; Plate IX, fig. 11; 



Plate XI, figs. 14 and 16. 



Specific Characters. — Shell produced transversely in adults, moderately gibbous, 

 evenly convex, more so comparatively in young forms. Anterior end short, about 

 one-fourth of the whole shell, with a regularly curved border meeting the hinge- 

 line above at an angle, but passing into the inferior border with a regular curve. 

 Inferior border broadly curved in its anterior half ; then becoming straight and 

 slightly sinuous. Posterior border bluntly rounded ; in older forms the junction 

 with the inferior border is somewhat angular. Hinge-line apparently slightly 

 arched, due to the meeting of the anterior and posterior parts at an obtuse angle. 

 The posterior end is regularly and evenly compressed into its lower and posterior 

 borders ; but above the posterior-dorsal slope is expanded, subcarinate, and slightly 

 concave above. Umbones obtuse and blunt, remote, varying slightly in position, 

 never central, somewhat raised above the hinge-line ; lunule small. Hinge-plate 

 narrow ; the anterior and posterior parts meet at a very wide angle. In the right 

 valve there is a small cardinal tooth just posterior to the umbo, with a pit behind 

 it, PI. IX, fig. 11. The posterior part of the plate is a narrow ledge, with a groove 

 above it for the ligament. Interior normal. Internal surface very smooth, marked 

 on the posterior slope by radiating lines. 



Surface in the two testiferous forms marked with very faint concentric lines 

 of growth. Periostracum much wrinkled. 



Measurements : 



Antero-posteriorly. Dorso-ventrally. Laterally. 



28 mm. 17 mm. 11*5 mm. 



Medium forms 20 „ 14 „ 10 „ 



Young forms 16 „ 12 „ 9*5 ,, 



Localities. — England : Hard-mine roof, North Staffordshire. Mountain Mine, 

 Wigan. Doe Hill, Nottingham. Leicester Coal-field. Coal-measures, South 

 Wales. Scotland : Limestone-Shale, Dunfermline. 



Remarks. — There is some resemblance between the species under description 

 and the figure given by Mr. R. Etheridge, jun., in the ' Quart. Journ. Geol. Soc.,' 

 vol. xxxiv, pi. ii, fig. 20, under the name of Antliracosia ? nucleus (Brown ?), but 

 he states that the specimen was too imperfect to give a description of it. It was 

 from the original locality of Captain Brown's JJnio and Pachyodon nucleus, the 

 description of which differs only from my form in the fact that it is said to possess 

 a posterior end elongated and acute, whereas I have never found a specimen which 

 can be considered to be acute. Mr. Etheridge, jun., considered it probable that 

 Brown's shell was identical with one form of Rhind's Axinus Pentlandicus, ' Age 



