226 



THE GEOLOGIST. 



Discina appears to have existed during almost the entire series of Palaeozoic 

 and Mesozoic periods up to the present day ; and it is probable that the animal 

 was not at any period the inhabitant of very deep_ water, for all the recent 

 species of Lingula and Discina, or those species with a horny shell, have pre- 

 vailed in the littoral zone, and do not appear to have descended deeper than 

 about eighteen fathoms. The reader is referred for more ample details to 

 Prof. Suess' admirable "Memoir on the Habitat and Distribution of the 

 Recent and Possil Brachiopoda," recently published in Yienna. 



XLV.— DisciN.A mTiDX. Phillips. PI. v., figs. 22-29. 



OrUcula 7iitida. PhiEips' " Geol. of York," vol. ii., p. 221, pi. xi., figs. 10-13, 

 1836, = 0. cincta, Portlock's " Report of the Geol. of Londonderry, &c., 

 pi. xxxii., figs. 15, 16, 1843, = D. bulla, M'Coy's " British Pal'seozoic 

 Fossils," pi. md., fig. 32. 



The shells composing this species are marginally circular, or elongated oval, 

 the posterior portion being rather narrower than the anterior one. The larger 

 or free valve is conoidal, or limpet-like, and more or less elevated, the pointed 

 apex being situated at variable distances between the centre and the posterior 

 margin, but it is not always the most elevated portion of the valve. The sur- 

 face of the shell is covered with numerous small irregular concentric wrinkles, 

 or striae. The smaller or lower valve is somewhat flattened, or slightly concave 

 towards its anterior margin, "vvith an oval-shaped foramen, surrounded by an 

 elevated convex margin, which extends from near the centre of the valve to a 

 variable distance from the posterior edge. This valve is likewise ornamented 

 with numerous small irregular concentric ridges, or wrinkles, with small 

 flattened interspaces. No interiors have been hitherto obtained ; while the 

 largest Scottish examples I have seen measured ten lines and a-half in length 

 by about the same in width, the depth or elevation of the larger valve being 

 about six Hues. 



After a lengthened examination of Discina cincta, as well as of Discina hu.Ua, 

 I could perceive no valid grounds for separating these two so-termed species 

 from D. nif ida ; and any one possessmg a sufficiently numerons series of specimens 

 of the last named form would, I think, soon perceive that Phillips' shell presented 

 every degree of elevation — from that of an almost depressed shell to that ex- 

 treme " inflated bubble-like form," described by Prof. M'Coy. I am therefore 

 quite disposed to concur in the Irish author's opinion when he considers 

 D. cincta as nothing more than the perfect condition of D. nitida ; for when the 

 outer surface of the last named shell is absent, which is often the case, the cast 

 is generally almost smooth, or marked only with a few faint concentric and 

 radiating Imes, a circumstance which has apparently led some palaeontologists 

 to believe that Phillips' shell was smooth, while that of Portlock's was concen- 

 trically striated. 



Discina nilida is a common species in certain Scottish localities. It occurs 

 at Bolston Place Burn, in Lanarkshire, at one hundred and seventy-three 

 fathoms below " Ell coal two hundred and thirty-nine at Gare ; two huudi-ed 

 and sixty-five at Belston Burn ; and three hundred and fifty-four at Raes Gill ; 

 all in Iho parish of Carluke * It is likewise found at Haw-hill, near Lesma- 

 liago ; Auchentib1)cr and Calderside, High Blantyre ; and Capel Rig, East Kil- 

 bride. In Renfrewshire, at Arden-quarry, Thoriiliebank. In Stirtingshire, at 

 Craigenglcn ; and in the Balgrochen Glen ironstone, etc. In Ayrshire, at Craigie, 

 near Kilmarnock; Cessnock, parish of Galston; and Netherfi eld, near Strath- 

 avou. in EilVshire, at Strathkcnny, St. Andrews, (S:c. In Haddingtonshire, at 



♦ lacTitical specimens are found in Pike and Adams county, IBinois, America. 



