560 BRITISH PAL/ZOZOIC FOSSILS. [CepHALopopa. 
the same space when larger ; all the ridges set with small spinulose tubercles, about as far from each other as 
the ridges are apart, and slightly extended transversely so as to form indistinct rows across the whorls, nearly 
direct on the sides, and with a slight backward wave on the periphery. Septa moderately concave, with nearly 
simple edges, having a slight backward wave on the prominent middle of the sides, nearly direct across the 
periphery. Diameter of rather small specimen one inch six lines; proportional antero-posterior diameter of 
last whorl °%,, diameter of inner edge of umbilicus ,, width of penultimate whorl =, width of mouth (greatest 
at middle) =. 
This species seems to be liable to considerable variation in form from pressure, and especially a flattening 
of the sides, which, however, is certainly not the normal form. I have not seen the siphon, but Martin places 
it a little within the outer edge. 
Position and Locality—Not very uncommon in the black beds over the main carboniferous limestone 
of Derbyshire 
NautiLus oxystomus (Piill.) 
Ref.—Phill. Geol. York. Vol. I. t. 22. f. 35, 36; de Kon. Anim. Foss. Bel. t. 49. f. 3. 
Desc.—Lenticular, very much compressed laterally; greatest thickness at the edge of the small shallow 
umbilicus, from whence the sides slope, almost flatly, to the thin, very acutely carinated periphery ; whorls about 
four, their edges distinctly visible in the umbilicus ; the mouth very elongate, lanceolate, embracing three-fourths 
of the sides of the penultimate whorl. Surface of inner whorl spirally suleated, of the outer turns smooth, or 
with extremely fine, obsolete transverse lines of growth, having a very strong forward wave in the middle, and 
asmall, slightly marked one at the sloping edge of the umbilicus. Internal casts shew the septa strongly arching 
forwards from the umbilicus to a flat, solid band, about two or three lines wide, produced by the internal cavity 
not quite reaching the edge; the last chamber occupies rather less than half the last whorl, and is marked by 
a narrow, deep sulcus, a little on the inner side of the middle, produced apparently by a corresponding ridge on 
the interior of the shell, of which there is no trace on the outside. Diameter of average specimen three inches, 
proportional antero-posterior diameter of mouth to the lateral edges ;;,,, width of penultimate whorl visible within 
the umbilicus ;, width of umbilicus 4, greatest transverse diameter of mouth about ;;, distance of the septa 
in the last whorl from each other two and a half lines. 
I have not been able to observe the siphuncle in this species, but according to de Koninck it is very 
small and nearly central a little outside of the middle. The inner whorl is scarcely embraced by the succeeding 
one, is not compressed, and has a broad, convex periphery ; the next has a much more acute periphery, and is 
correspondingly embraced by the succeeding turn. 
Position and Locality—Rare in the carboniferous limestone of Lowick, Northumberland. 
Nautixus (Discites) QuUADRATUS (/em.) 
Ref. and Syn.—Flem. Brit. Anim. = (IV. bicarinatus M. V. K. Geol. Russ. t. 25. f.10. =. Verneuilanus d’Orb. 
Prod. p. 110.) = NV. swbsulcatus Phill. Geol. York. Vol. II. t. 17. f. 18 and 25; Geol. Trans. Vol. V. t. 40. 
f.'7; de Kon. Anim. Foss. Bel. t. 30.f.6; t. 47.£.9; t. 49. f. 4. 
Dese.—Discoid, compressed, of little more than two volutions; section of the whorls subquadrate ; the sides 
and periphery nearly equal in width, flattened, and at right angles; the sloped sides of umbilicus very steep, and 
about as wide as the inner margin between them ; periphery usually flat in the middle, and very slightly sloping 
at the sides towards the lateral angles, each lateral fourth bearing from one to five fine thread-like ridges (most 
usually the former number) ; sides sometimes nearly flat, on the half near the umbilicus moderately convex ; and 
the outer half moderately concave; but many specimens having each side obtusely ridged along the middle 
by two broad shallow sulci, while a few rare specimens have the sides divided into five coarse, subequal ridges, by 
three wider concave sulci; occasionally also the middle part of the periphery more prominent than the lateral 
