66 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



Specific Characters. — Shell subrotund, tumid ; the anterior part almost equal to 

 the posterior in size. Anterior, inferior, and posterior borders rounded ; its posterior 

 inferior angle less regularly curved than the rest of the margin. Umbones central 

 or slightly subcentral, tumid, obtuse, separated and raised above the hinge-line, 

 which is slightly arched, with the convexity upwards. Lunule distinct and 

 elongated. Ligament external, nearly as long as the posterior part of the hinge- 

 line. Surface with concentric striae and lines of growth. Periostracum thick and 

 much wrinkled. Interior unknown. 



Dimensions : 



Antero-posteriorly . . . .31 mm. 



Dorso-ventrally . . . .23 mm. 



Laterally . . . . .21 mm. 



Localities. — Banbury Seam, Adderley Green, Longton, North Staffordshire. 

 Oldham ; Lowmoor, Bradford ; Wednesbury Oak. 



Observations. — The figures of TJnio and Pachyodon Dawsoni (Brown) are very 

 characteristic of entire specimens of this shell ; those of U. or P. subrotundus are 

 typical of crushed forms, giving rise to the appearance of alse on each side, and 

 forcing the umbo to one side or other. 



The form is very characteristic, and seems to vary less than any other species 

 of this genus. I consider it to be a rare form ; and, although Captain Brown 

 quotes the occurrence of this species from Lowmoor and Oldham, I have not met 

 with any specimens except in North Staffordshire, neither have I come across 

 examples in any museum. 



The figured specimens all show much wrinkling of the periostracum, which 

 was probably, therefore, very thick. I have several other specimens from the same 

 locality, but they are much crushed, and when in this condition resemble Brown's 

 figure of TJnio Daivsoni. I have adhered to the name " subrotunda" as the figure 

 by which U. subrotundus is represented is one of a much more perfect specimen 

 than that of U. Daivsoni. 



11. Carbonicola turgida {Brown). Plate VIII, figs. 8 — 25. 



Pachyodon tubgidus, Brown. Annals Mag. Nat. Hist., vol. xii, 1843, p. 394, 



pi. xvi, figs. 13, 14. 



— dubius, Brown- Ibid., p. 392, pi. xvi, fig. 5. 



— similis, Brown. Ibid., p. 393, pi. xvi, fig. 12. 



— Blatdsii, Brown. Ibid., p. 394, pi. xvi*, fig. 2. 



Unio tuegidus, Brown. Fossil Concbology, 1849, p. 178, pi. ixxiii, figs. 10, 17. 



— dubius, Brown. Ibid., p. 177, pi. Ixxiii, fig. 13. 



— similis, Brown. Ibid., p. 178, pi. Ixxiii, fig. 9. 



— Blatdsii, Brown. Ibid., p. 178, pi. Ixxiii, fig. 2. 



