CrrHALopopa. | UPPER PALAZOZOIC MOLLUSCA. 561 
thirds, and concave (sometimes all these varieties in a single specimen). Surface crossed by very minute sigmoid 
strize on the sides, arched backwards on the inner half, also strongly arched backwards on the middle of the 
periphery (where in perfect preservation the transverse strize are crossed by minute spiral ones under the lens). 
Septa moderately numerous, their edges gently arched backwards on the sides and periphery ; body chamber 
occupying half of the last whorl; siphon small, close to the outer edge. Diameter one inch seven lines; pro- 
35 30 
portional thickness, or width of mouth at edge of umbilicus, =, width of periphery =, diameter of inner edge 
of umbilicus ;4,, antero-posterior diameter of mouth ;;,, distance of septa apart in last whorl one line. 
The originally described type of Dr Fleming (resembling de Koninck’s, t. 49, f. 4) is common in Scotland, 
and has the periphery almost or quite as wide as the sides, its lateral keels being very fine, and the lateral fourths 
not perceptibly sloping ; the sides also being flat and without distinct sulci; the passage, however, is imperceptible 
between such specimens and those with an obtuse spiral ridge in the middle of each side; and from these again 
into the forms with the lateral fourths of the periphery sloping, leaving the middle half elevated and concave. 
The variety with five sulci on the sides is very rare, but one of the Lowick specimens combines most of the above 
varieties ; and having the middle of the periphery elevated and channelled on the inner whorls, but flat on the 
outer ones, shews that this difference is independent of age. Like many of this subgenus (Discites) the 
body-whorl in old specimens is slightly disjoined. 
Position and Locality—Common in the carboniferous shale of Craige, Kilmarnock; carboniferous lime- 
stone of Lowick, Northumberland. 
NaAutTiLus (Discites) sutcatus (Sow.) 
Syn. and Ref.—Sow. Min. Con. t. 571. f. 1 and 2; Phill. Geol. York. Vol. II. t. 22. f. 31,32; =(N. sul- 
cifer +N. dorsatus) L’Ey. Mem. de la Soc. Geol. de France, Vol. I. t. 2. f, 1 to 4. 
Dese.—Discoid, moderately compressed ; of two and a half gradually increasing whorls, completely exposed 
in the deep, almost vertical-sided umbilicus; greatest thickness of the whorls at the edge of the umbilicus, 
from whence the sides gradually conyerge to the sharply-defined, narrow periphery, which is moderately concave 
between the two bounding keels; the outer half of each side of the whorls is occupied by two deep, concave, 
spiral sulci, each only slightly narrower than the periphery, the inner more prominent half of each side, towards 
the umbilicus, seems simple in ill-preserved specimens, but is split into three equal ridges by two narrow sulci in 
all moderately well-preserved examples; all the sulci indistinct near the mouth of old specimens. Surface 
crossed by very fine, transverse strize of growth; retroflexed on the periphery and on the middle of each side, 
the flexures strongest in old specimens; last chamber occupying half of the body-whorl; septa moderately 
numerous. Diameter of average specimen one inch seven lines, proportional antero-posterior diameter of mouth 
* diameter of umbilicus “4, width of periphery at mouth *4, width of mouth at edge of umbilicus {;, or 
slightly more. 
This species is easily distinguished by its narrow, sharply-defined periphery, and the two very broad 
and two small spiral grooves on each side. All authors describe the siphon at some point between the centre 
and outer margin, but I have not been able to see it. 
Position and Locality—Rare in the carboniferous limestone of Kendal, Westmoreland. 
Nautitus (Discites) TRocHLEA (M/*Coy). Pl. 3. H. fig. 16. 
Ref—M Coy, Synop. Carb. Foss. Irel. t. 3. f. 4. 
Dese.—Discoid, of two and a half rapidly enlarging whorls, almost entirely exposed in an umbilicus, with 
vertical sides; sides of the shell nearly flat, sloping with slight convexity from the rectangular edge of the 
umbilicus to the narrow, deeply-concave periphery, which is bounded by two acutely angular edges; mouth 
widely trigonal, notched at apex by the concavity of the periphery ; septa moderately numerous, having a broad 
backward curve on the sides, and a more abrupt one on the periphery, the two separated by an acute forward 
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