20 ORDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



2. Oxydiscus bougangensis, sp. iiov. Plate IV, fig. 3. 



Specific Characters. — Shell liigli, narrow, lenticular, nuicli compressed, of 3 — 4 

 whorls, dorsally acute. Umbilicus small, moderately deep, about one-fifth the 

 diameter of the shell and situated at less than half its height. Outer whorl 

 rapidly increasing in height, large, embracing fully three-fourths of precedmg 

 whorl, more than twice as high as wide ; sides gently convex, more or less flattened, 

 rising to a much compressed very acute sharp dorsal ridge ; umbilical edge abruptly 

 subrectangular ; umbilical slope short, vertical. Surface smooth ? 



Dimensions. — Height of shell about 30 mm. 



Horizon. — Lower Ordovician : Stinchar Limestone Group. 



Locality. — Bougang, Knockdolian, Ayrshire. 



Uemarlis. — This shell maybe compared with 0. suhacutus, Ulrich,^ but in ours 

 the outer whorl is larger and embraces the preceding whorl to a greater extent. 

 The surface is not sufficiently preserved to determine the character of the orna- 

 mentation. The type specimens are in Mrs. Gray's Collection. 



3. Oxydiscus hunteri, sp. nov. PI. IV, figs. 4-8. 



Specific Characters. — Shell lenticular, dorsally acute, composed of 4 — 5 whorls. 

 Umbilicus large, rather shallow, exposing all the inner whorls, about two-fifths 

 the diameter of the shell and with its centre situated below the middle of the 

 shell ; umbilical edge abru]jtly rounded to subrectangular ; umbilical slope 

 vertical. Whorls scarcely overlapping ; higher than wide, subtriangular ; outer 

 whorl large, gradually increasing in size to mouth, embracing less than half 

 height of preceding whorl, sublanceolate in cross-section, swollen towards base, 

 then becoming slightly concave at base of high narrow compressed solid carina. 

 Surface of shell ornamented Avitli closely-placed transverse lines of somewhat 

 unequal strength strongly arched back, oblique to umbilical edge, and meeting 

 carinal edge at about 30" — 45°, having somewhat irregularly developed short 

 fine wrinkles set at right angles to them in interspaces, producing a minute cancel- 

 lation. Mouth sloping obliquely backwards. 



Dimensions. — i ii 



Height of shell . . 26-0 mm. . . . about 17-0 



Height of outer whorl 



without carina at mouth 12-0 ,, (ditto with carina) . 7'0 

 Width of ditto at mouth, 



about 10"0 „ . . . about 5*5 



Horizons. — Lower Ordovician : (I) Balclatchie Group (conglom.) ; (2) ? Stinchar 

 Limestone Group. 



Localities. — (1) Balclatchie, Girvan ; (2) Aldons, near Girvan. 



1 Uliich aud Scoiield, op. cit., p. 913, pi. Ixii, figs. 62—65; pi. Ixxxii, figs. 23—25. 



