332 CARBONIFEROUS LAMELLIBRANCHIATA. 



sulci becoming also less well marked. In the better preserved specimens granular 

 markings are seen over the valves, especially on the posterior slope. 



Dimensions. — Fig. 10, PI. XXXVII, from the Pennystone Ironstone, Coal- 

 brookdale, in my Collection, measures — 



Antero-posteriorly . . . .74 mm. 



Dorso-ventrally . . . .34 mm. 



From side to side . . . .25 mm. 



Localities. — England : the Peunystone Ironstone, Coalbrookdale. A band 

 containing a marine fauna. 



Observations. — This shell was described by J. de C. Sowerby, in an appendix 

 to Prestwich's ' Geology of Coalbrookdale,' under three specific names ; the very 

 young shell being described as Nucula accipiens, while the well-sulcated full-grown 

 shell was erroneously referred to the JJnio figured by Ure (' History of Ruther- 

 glen,' p. 311, pi. xvi, fig. 4) as JJnio Urei, and a variety with the concentric rugaa 

 more split up into lines and strias was named JJnio parallelus. The JJnio of Ure is 

 Carbonicola aquilina, and is perfectly distinct from the species under discussion; 

 moreover it has never yet been found in association with marine fossils. This 

 specific name cannot be retained, and the term accijnens is adopted as it is the 

 prior one on the page of description. 



Professor Amalizky placed the name JJnio JJrei as a possible synonym of his 

 Naiadites Verneuili, a genus of fresh- water edentulous shells allied to Carbonicola, 

 but not belonging to Naiadites, Dawson. 1 This was of course due to a mistake 

 arising from the comparison of figures, and partly due to the very meagre 

 description of JJnio JJrei originally given. 



There appear to be two well-marked forms of this shell, one of which, like the 

 type of JJnio JJrei, has well-marked sulcations, and rugae only becoming linear 

 near the lower border; the other like the type of JJnio paraUelus, where the ruga3 

 and sulci are somewhat obscure, and they tend to split up even in the upper part 

 of the shell : but in shape and size the two forms are identical, and all gradations 

 of external ornament exist between the extremes. I have, therefore, decided to 

 unite the two species. In the original figures the posterior ends of both forms 

 are incomplete. The postero-superior angle of the type of JJnio JJrei has gone, 

 and a great deal of the posterior end of the type of JJ. parallelus is absent. An 

 examination of the curvature of the lines of growth will demonstrate at once that 

 the posterior end in both forms is rounded, but this is rarely seen owing to the 

 incomplete preservation of the shell above and behind. Fig. 15, PI. XXXVII, 

 however, shows the real shape of the contour of the posterior end. The valves 

 are often crushed, and this often gives rise to a false appearance of an oblique 

 ridge, — in fact, it is very rare to find a perfect specimen. 

 1 ' Quart. Journ. Geol. Soe.,' vol. 1, p. 439. 



