BUCANIA GRAVIDA. 31 



1. Bucania evoluta, sp. nov. Plate VI, fig. 6. 



Specific Gharacters. — Shell composed of 3 — 4 whorls rather loosely coiled, 

 scarcely overlapping, rapidly increasing in size, rather higher than wide, snb- 

 elliptical in section. Outer whorl rather rapidly increasing in height to month, 

 with dorsum bearing narrow, strongly elevated keel; sides gently convex, with no 

 umbilical edge. Umbilicus shallow, exposing all the whorls, with centre situated 

 at about one-third height of shell. Surface cancellated, being marked with thick, 

 low rounded, oblique spiral lines closely placed, directed forwards to meet slit- 

 band at 45° — 30°, and crossed by a few widely separated transverse sublamellose 

 ridges (? fimbriated) and by finer lines arched back and meeting slit-band at about 

 G0°— 75°. 



Dimensions. — Height of shell, 14"0 mm. ; width of Avhorl near mouth, 7'5 mm. 



Horizon. — Lower Ordovician : Balclatchie Grroup (Conglomerate). 



Localitij. — Balclatchie, Girvan. 



Remarks. — There is only one specimen of this species, and the ornament is 

 only partially preserved. It seems to resemble B. subangulata, Ulrich,^ but is 

 higher and more compressed, and the whorls overlap less than in that species. 



2. Bucania gravida, sp. nov. Plate VI, figs. 7- — 9. 



Specific Gharacters. — Shell discoidal, subglobose, composed of 3 — 4 low 

 transverse whorls slowly increasing in size to mouth. Umbilicus subcentral, 

 deep, exposing inner whorls, with sharp angular umbilical edges and steep 

 flattened umbilical slopes. Whorls transverse, wider than high ; dorsum broad, 

 gently convex or somewhat flattened, with the umbilical edges limiting it 

 and situated at about half the height of the whorl. Slit-band narrow, slightly 

 raised. Surface of whorls crossed by transverse strong subequidistant rather 

 remote growth-ridges or lines meeting the slit-band at about 60°, with the broad 

 interspaces occasionally crossed by very delicate minute and somewhat sinuous 

 striae at right angles to the transverse ridges and interrupted by them. 



Dlmensiuns. — Height of shell, 12 — 14 mm. ; width of whorl near mouth, 

 11 — 12 mm. 



Horizons. — (1) Lower Ordovician: Stinchar Limestone Group; (2) Lower 

 Ordovician : Balclatchie Group. 



Localities. — (1) Craighead, Girvan ; (2) Balclatchie, Girvan. 



RemarJiS. — This species seems related to Bucania contorla (Eichw.)^ in shape 

 and general characters from stages C and D in the Baltic Provinces. The 



1 Ulrich aud Scofield, o^. cit., p. 891, pi. Ixvi, figs. 20 — 23. 



2 Eichwald, ' Leth. Eoss.,' vol. i, pt. ii (1860), p. 1072, pi. xli, figs. 3 a, 6; Kokeu, ' Gastrop. 

 Bait. Uiitersilurs,' p. 123. 



