556 BRITISH PALAZOZOIC FOSSILS. [CePHALOPopDA. 
Porcettia Puzost (L’ Ev.) 
Ref—Meém. de la Soe. Géol. de France, Vol. II. t. 2. f. 10, 11; de Kon. Anim. Foss. Bel. t. 28. f. 1. 
Dese.—Discoid, whorls four, subpentagonal, barely touching; periphery very broad, moderately convex, 
with a strongly marked, narrow, median, cord-like keel ; sides steeply sloping into the umbilicus, most prominent 
at the junction of the sides with the periphery, where the two outer whorls are crowned with very prominent 
conoidal tubercles, lengthened in the direction of the centre about half way to the edge of the umbilicus ; 
compressed anteriorly and posteriorly, and separated by rather wider concave spaces ; about fourteen tubercles 
on the outer whorl at a diameter of one inch three lines, about ten on the outer whorl at seven lines in diameter, 
the two inner whorls destitute of tubercles. Surface marked with strong spiral lines of small equal tubercles, the 
rows in large specimens imperfectly alternating in size (eleven or twelve rows in the space of one line), the 
granules so arranged that they fall into lines either spirally or transversely. Diameter of average specimen 
49 15 
one inch three lines, width of mouth at apex of tubercles {%, at inner edge ,;,, width of umbilicus at inner 
edge of body-whorl +, antero-posterior diameter of penultimate whorl =. 
Position and Locality—Not uncommon in the dark carboniferous limestone of the Isle of Man; abundant 
of small size in the the carboniferous shales of Craige, near Kilmarnock; rare in the carboniferous limestone 
of Derbyshire. 
2nd Family. NAUTILIDA. See page 311. 
Genus. NAUTILUS. (ZLinn.) 
Gen. Char.—Shell globose, involute, more or less compressed laterally ; last chamber very large, usually 
much embracing the preceding ones ; septa simple, or gently waved backwards on the sides and periphery ; 
siphon usually subcentral, but varying from the inner to the outer edge. 
Common from the Paleozoic to the Eocene tertiary inclusive, rare in the newer tertiaries and recent seas. 
There are three subgenera: 1. Discites (M°Coy), formerly proposed for those compressed species 
with flattened, quadrate whorls, exposed in a wide umbilicus, having the siphon near the outer edge, the 
periphery narrow, often concave, and the septa arched backwards on the sides and periphery. This section, 
in which the last whorl often becomes slightly disjoined, occurs in the Devonian, and very commonly in 
the Carboniferous rocks. 2. Cryptoceras (d’Orbig.), in which the whorls are entirely embracing, and the 
septa nearly simple, as in the true Vautilus, but the siphon placed at the outer margin. This section has 
few species all Paleozoic. 8. Atwria (Bronn), having the general form of the true Vautilus, but the siphon 
at the inner edge, and the septa with a deep, tongue-shaped lobe on each side; this section is exclusively 
Eocene Tertiary. The typical Nawtili have the whorls entirely embracing, or nearly so; the septa simple 
or slightly waved, and the siphon subcentral. 
NAUTILUS BILOBATUS (Sov.) 
Ref. and Syn.—Sow. Min. Con. t. 249. f. 2, 3.= Nautilus clitellarius Sow. Geol. Trans. 2nd Series, Vol. V. 
t. 40. f. 5; M. V. K. Geol. Russ. t. 25. f. 11. 
Desc.—Globose ; of two to three very rapidly enlarging whorls; mouth very broad, transversely reniform, 
obtusely rounded at the sides; greatest width of the shell at the edge of the umbilicus; periphery broadly 
rounded, with a nearly semicircular section, very slightly flattened at the middle ; umbilicus small, very deep, 
exposing about a third of the inner turns ; surface of the inner whorls marked with fine spiral strize, crossed by 
very fine transverse strize of growth (the spiral striae seem to disappear on the large specimens); septa very 
numerous, about two lines apart in the middle, at an inch and half in width, one line apart at five lines in width, 
their edges extending from the umbilicus towards the periphery, with a broad slight curve, the convexity 
backwards; on reaching the middle third of the periphery, they abruptly bend forward with a tongue-shaped 
semielliptical curve, extending so far forwards, that a straight line extending from the septum at the middle of the 
