Creruacopopa.] UPPER PALAXOZOIC MOLLUSCA. 573 
Orruoceras (7rigonoceras) PARADOXICUM (Sow.) 
Rtef—Sow. Min. Con. t. 457. 
Desc.—Rapidly tapering, abruptly incurved towards the smaller end, forming about half of a volution ; 
external face gently concave, bounded by strong angles (slightly less than rectangular) ; lateral faces equal to 
the external one in width, converging to a strong keel along the middle of the inner face, the outer half of the 
lateral faces flattened, the inner half of each abruptly rounded nearly to a quarter of a circle ; surface under the 
lens marked with minute, subequal, slightly flexuous longitudinal strize (about thirty in the space of two lines) ; 
a few stronger longitudinal ridges on the lateral keels of the external face ; lines of growth indistinct, broadly 
arched backwards on the external face, and converging at a very acute angle, directed backwards, on the internal 
keel. A specimen of last chamber, imperfect at each end, two inches long, has the lateral faces one inch four 
lines wide at the large end, and one inch wide at the smaller, the exterior face being one inch three lines 
wide at the large end; septa moderately convex; siphon a little eccentric towards the external side. 
I have seen only one perfect specimen, in the collection of my friend the late Major Sirr: it exhibits the 
inrolled posterior extremity above alluded to. The specimen in the University collection shews the striation of 
the surface preserved, which I had not seen before. 
Position and Locality—Rare in the dark carboniferous limestone of the Isle of Man. 
OrtHoceras (Cycloceras) RuGosuM (F lem.) 
Ref —F leming, Thomson’s Annals of Phil. Vol. V. t. 31. f. 9. 
Dese.—Subcylindrical, and nearly straight when old, abruptly and irregularly tapering, and moderately 
curved towards the small end; section circular; surface girt with equal, obtusely rounded, very prominent, 
irregularly waved, slightly oblique rings (having two septa in the space between each pair of rings) ; inter- 
annular spaces flat, and slightly more than twice the thickness of the rings in width ; rings nodulated by the 
crossing of about twenty-six equal, filiform, slender, tuberculated ridges, separated by flat spaces, nearly twice 
their width, such spaces being at least twice as long as wide (four ridges and three intervening spaces equalling 
the space from the centre of one transverse ring to the other); septa moderately convex; siphon very minute, 
close to the margin (coinciding with the convex aspect of curved specimens, and at the higher edge of the septa 
and external rings). Specimens five lines in diameter have their rings two lines from centre to centre; 
specimens one inch in diameter have their rings on the sides, about three lines from centre to centre, but five 
lines on the exterior, and only two lines on the inner aspect of curved specimens. 
This species tapers so irregularly, and the fragments are so short, that any measurements of their pro- 
portions would be deceptive. Some of the large specimens shew traces of very fine, close, transverse striz. 
Position and Locality —Rare in the black marble beds over the main limestone of Derbyshire ; rare in the 
carboniferous limestone of Lowick, Northumberland. 
OrRTHOCERAS (Loxoceras) SOWERBYI (J/‘Coy). 
Ref. and Syn. = O. undulatum Sow. Min. Con. t. 59. (not of Schlot. nor O. laterale Phill.). 
Desc.—Gradually tapering at the rate of about two lines in one inch; section usually oval, but the 
amount and direction of the compression variable. Septa very approximate, oblique, very slightly waved 
forwards on one side, and backwards on the other, with a slight sigmoid curve on the sides; moderately 
coneave, averaging ten interseptal spaces in the mean diameter, when that varies from one inch and half, to 
one inch ; siphon moderately large, about one sixth of the diameter from the most posterior edge. Surface 
marked with minute strie of growth, obliquely inclined in the opposite direction to the septa. 
The compression of this species being so variable, and all our specimens having the siphon on the 
transverse, instead of on the conjugate axis, I am inclined to believe the elliptical section in some measure 
