OXYDISCUS PEHTlIRIiATUS. 21 



Remarks. — Most of the Balclatcliie specimens occur as internal casts and in 

 such the solid carina is not represented, but in one specimen (fig. 4) in Mrs. Gray's 

 Collection the shell is fortunately preserved and we see the nature and relations of 

 the carina and the character of the ornamentation. The affinities of the shell are 

 undoubtedly with 0. siibacntus, Ulrich,i and probably with 0. annuhms, Perner, 

 though in the high narrow carina it is more like 0. {Cyiiodiscus) procer, Barr.' 

 The course of the transverse lines is like that of 0. Huhacufns, but the fine cross 

 wrinkles are more like those of (U/rtuJlfef< suJ}pl(inHS, Ulricli,* and (JiirtoliUiria 

 nUidnla, Ulrich.^ There is no slit-band visible on the keel, and this separates it 

 from Zonidiscus to which at first sight it might l^e thought to belong. 



The typical examples of 0. hinitcri are in Mrs. Gray's Collection from 

 Balclatcliie. 



4. Oxydiscus ? perturbatus (Sowerby). 



? 1839. Euomphalus tenuisfriatus, Sowerby iu Miircliisou's Silurian System, p. 641, pi. xxii, fig. 14. 



1839. Euomphalus j)erturbatus, Sowerbj, ibid., p. 641, pi. xxii, fig. 15. 

 ? 1846. Euomphahis furcatus, McCoy, Syn. Silur. Foss. Ireland, p. 13, pi. i, fig. 11. 

 1859. Bellerophon ijerturhatus, Sowerby in Murcliison's Siluria, 2nd edit., p. 218, Foss. 39, fig. 6. 

 1866. BeJlerophon i)erturbalus, Sowerby, Salter, Mem. Geol. Surv., vol. iii, p. 350, woodcut 16; 



ibid., 2nd edit. (1881), p. 557. 

 1884. Belleropihon perturbatus, Sowerby, J. D. La Touclie, Handboolc to the Geolugy of Shropshire, 

 p. 57, pi. ii, fig. 46. 



8]iecific Characters. — Shell coiled rather loosely, discoidal, composed of about 

 five whorls in contact but scarcely overlapping each other, enlarging gradually, the 

 outer whorl more rapidly increasing in height to mouth. Umbilicus open, rather 

 shallow, exposing all the inner whorls, situated rather below centre of shell. 

 Whorls higher than wide ; sides rounded, somewhat swollen at base ; dorsum sub- 

 angular and weakly carinate in early part of outer whorl but becoming less so 

 towards mouth. Mouth high, with very shallow open dorsal sinus. Surface of 

 shell crossed by closely-placed equidistant or subequidistant regular equal trans- 

 verse strong lines arched back gently in simple curve obliquely directed to dorsal 

 carina, which they meet at about 75° or less, uniting with those of opposite side ; 

 interspaces occasionally show several fine intermediate striae. 



Dimensions. — Height, about 10 mm. 



Horizon. — (1) Lower Bala (Llandeilo Flags) ; (2) Arenig Series. 



Localities. — (1) Pensarn, Caermarthen ; Middleton, Corndon ; ? Shelve ; (2) Bath 



House, Bangor ; Long Plantation cutting, Haverfordwest. 



1 Ulrich and Scofield, op. cit., p. 913, pi. Ixii, figs. 62 — 65. 



- Perner, op. cit., p. 74. pi. Ixxxvi, figs. 1—3. 



3 Ibid., p. 74, pi. Ixxxviii, figs. 22-24, text-fig. 50. 



* Ulrich and Scofield, op. cit., pi. Ixii, figs. 40 — 44. 



5 Ibid., p. 866, pi. Ixii, figs. 53—55. 



