66 CARBONICOLA, ANTHRACOMYA, AND NAITADITES. 
Specifie 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 striz 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 Unio and Pachyodon Dawsoni (Brown) are very 
characteristic of entire specimens of this shell; those of U. or P. subrotwndus are 
typical of crushed forms, giving rise to the appearance of alz 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 Unio Dawsoni. 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. Dawsoni. 
11. Carponicota turGIpa (Brown). Plate VIII, figs. 3—25. 
PacHyopon TuRGIDUS, Brown. Annals Mag. Nat. Hist., vol. xu, 1848, p. 394, 
pl. xvi, figs. 13, 14. 
a puBius, Brown. Ibid., p. 392, pl. xvi, fig. 5. 
siminis, Brown. Ibid., p. 393, pl. xvi, fig. 12. 
— Braypst, Brown. Ibid., p. 394, pl. xvi*, fig. 2. 
Unto turatous, Brown. Fossil Conchology, 1849, p. 178, pl. lxxii, figs. 10, 17. 
— pusBius, Brown. Ibid., p. 177, pl. Ixxiii, fig. 15. 
—  siitis, Brown. Ibid., p. 178, pl. Ixxiui, fig. 9. 
— Buaypsu, Brown. Ibid., p. 178, pl. lxxiii, fig. 2. 
