CrepHatopops. | UPPER PALAZOZOIC MOLLUSCA. 567 
Var. B. crenistria. 
Ref. and Syn. = Goniatites crenistria Phill. Geol. York. Vol. II. t. 19. f..7, 8, 9. 
Desc.—Septa and striation as in the typical form, but the sides moderately compressed; and sometimes slight 
extensions of the serrated edges of the strie form interrupted spiral lines. Average diameter one inch seven 
lines, proportional diameter of umbilicus 44, width of mouth varying from # and & to # and ¥%; transverse, 
flat, serrated, striae averaging seven in one line, at middle of specimen one and half inches in diameter. 
The only difference between this and the typical A. sphwricus is the more compressed form, which the pro- 
portional measurements given above, of specimens differing little in size, shew to be very variable. I at one 
time thought the proportion of the mid-lobe which would be cut by a line connecting the apices of the first lateral 
sinus of each side, might serve to separate the species from the true sphwricus, but I now find that this 
character, depending on the closeness of the septa, varies irregularly in different parts of the one specimen. 
The variety y. striatus (A. striatus of Sowerby) is not in the collection; it only differs from the var. 
crenistria by having spiral striz stronger than the transverse ones; it has been united with the G. crenistria 
by de Koninek, with much propriety, I think, The Ammonites minutus Sow., supposed by de Koninck to be 
the young of the A. sphwricus, is a cretaceous fossil. 
Position and Locality—Common in the carboniferous limestone of Derbyshire; common in the car- 
boniferous limestone of the Isle of Man. 
AGANIDES SPIRORBIS (Gib. Sp.) 
Ref. and Syn.=Goniatites spirorbis Gilb. Phill. Geol. York. Vol. If. t. 20. f. 51 to 55. 
Dese.—Discoid, flattened, of seven and a half rounded whorls, moderately embracing, but leaving one half of 
their width exposed in the very wide shallow umbilicus ; the innermost half whorl dilated, forming a Nawtiloid 
nucleus; sides of the whorls yery convex; edge of the umbilicus very narrow, abruptly rounded; mouth semi- 
elliptical, indented by the preceding whorl; periphery narrow, rounded. Surface crossed by fine transverse 
striae. Septa (indistinctly seen): mid-lobe wider than long, with converging sides, and broad obscurely trifid 
extremity ; first lateral sinus obtusely trigonal, rounded at the extremity, rather wider at base than long; first 
lateral lobe wide, rotundato-trigonal, shorter than the mid-lobe; second lateral sinus scarcely arched, nearly 
perpendicular to the edge of the umbilicus, into which it runs. Average diameter from two to three lines, pro- 
portional width of umbilicus about ;{;, width of last whorl ,{3. 
Position and Locality—Not very uncommon in the black carboniferous limestone of the Isle of Man, 
Genus. ORTHOCERAS. See p. 312. 
Ortuoceras (Loxoceras) Breynt (Mart. Sp.) 
Ref. and Syn.= Conch. N. Orthoceratites Breynit Martin, Pet. Derb. t. 39. (not of Sow. Min. Con.). 
Desc.—Rapidly tapering (at an angle of about 14°); moderately depressed, section broad-oval. Septa 
from last chamber, to four lines in diameter, averaging five to six in the space equal to a diameter; very slightly 
oblique on the narrow sides, slightly higher or more anterior on one of the broad sides, which they cross 
with a scarcely perceptible wave towards the mouth; a little lower or more posterior on the other broadside, 
in the middle of which is a strong backward wave, near to which the siphuncle is placed on the conjugate 
axis. Siphuncle small, and a little within the margin, where it passes through the septa, but dilated between 
them into depressed spheroidal beads, about twice as wide as long, and touching the surface throughout the 
length of the shell; interior of the siphon traversed by a small continuous tube, attached to the inner walls 
of the dilated portion by radiating, vertical, shelly partitions (about eight in a whorl), constricted by transverse 
stronger partitions in the middle of each dilatation (or intermediate between the septa). Surface (indistinct) 
apparently marked with fine, obtuse, transverse striae. The proportion of the long and short diameter of the 
[rasc. 11. ] 4D 
