564 BRITISH PALAXOZOIC FOSSILS. [CEPHALOPoDA. 
mouth semielliptical, deeply indented by the preceding whorl; surface crossed by transverse strie, very 
variable in size (six in two lines on average specimens, one inch in diameter, but often finer), nearly direct and 
simple on the young whorls, but di- or tri-chotomous near the edge of the umbilicus on the old ones, in which 
they are gently sigmoid on the sides, and have a broad, shallow, backward wave on the periphery ; occasionally 
two or three constrictions on the cast, coinciding in direction with the striee. Septa: mid-lobe slightly broader than 
long, with diverging sides, trifid ; the middle lobules less than half the length of the lateral ones, which are only 
half its whole length; first lateral sinus broadly rounded at the end, with sub-parallel sides narrower than the 
mid-lobe; first lateral lobe small, linguiform, pointed, a little longer than wide, scarcely exceeding the mid-lobe in 
length; second lateral sinus reaching nearly to the height of the first, extending with slight convexity into the 
umbilicus. Diameter of average specimen one inch two lines, diameter of umbilicus =, width of mouth 
at edge of umbilicus = to =. 
The extreme flattened varieties noticed on the continent have a width of mouth at umbilicus of only ;*,, and 
20 
a diameter of umbilicus of only 3); these are generally large specimens. The thickest extremes have the 
umbilicus “°, and the width of mouth at umbilicus =. Our specimens do not shew the septa distinctly, 
but in external characters are perfectly identical with the continental examples. Most foreign authors quote the 
Goniatites striatus of Phillips as a variety of this species, of which his small figures are very possibly the young, 
but his figures 14 and 19 by no means agree with the species in question. The last chamber occupies nearly 
all of the last whorl. The greater compression, smaller umbilicus, finer striae, and want of the large tubercles 
on the edge of the umbilicus, distinguish this species from the A. Listeri. 
Position and Locality—Very common in the limestone nodules of the coal-shale near Halifax. 
AGANIDES GILBERTSONI (Phill. Sp.) 
Ref. and Syn. = Goniatites Gilbertsoni Phill. Geol. York. Vol. II. t. 20. f. 27 to 31. 
Dese.—Lenticular, much compressed, sides gently convex, greatest thickness close to the umbilicus, sloping 
gently from thence to the periphery, which is narrow and rounded ; umbilicus very minute, not exposing the 
inner whorls; surface nearly smooth, crossed with microscopic sigmoid strie. Septa close, regular; mid-lobe 
extremely wide, deeply bilobed, the intervening sinus bifid, oblong, a little longer than wide, and alone occu- 
pying the periphery; lateral portions of the mid-lobe broader than the sinus on the periphery, deeply bilobed, 
and placed upon the sides; first lateral sinus narrow, parallel-sided, rounded at tip, extending about as far 
forward as the end of the notch in the lateral part of the succeeding mid-lobe; usually two strong lateral 
spiral sulci on the casts coincide with the outer sides of the mid-lobe and first sinus ; first lateral lobe of moderate 
length, elliptically pomted, obtuse, scarcely as long as the lateral parts of the mid-lobe; second lateral sinus 
broad, strongly arched. Average diameter six and half lines, proportional diameter of umbilicus ;;,, width of 
mouth at umbilicus “4, width of periphery about 5. 
The septa of this species are very anomalous in any point of view, but less so if we view the bifid portion of 
the septa on the periphery, and the next bifid portions on the sides as parts of one great mid-lobe, as I have 
done above, than if we follow Professor Phillips, and consider the bifid peripheral portion as the homologue of 
the bifid mid-lobe of other species of the genus, which on this latter view would be directed towards the mouth 
instead of from it: the direction of the large second lateral sinus at the margin of the umbilicus is entirely in 
favour of my proposed mode of viewing these inflections. 
Position and Locality—Not uncommon in the black carboniferous limestone of the Isle of Man. 
AGANIDES HEnstowr (Sow. Sp.) 
Ref. and Syn.= Ammonites Henslowi Sow. Min. Con, t. 262. 
Desc.—Discoid, compressed, of fiye or six very gradually increasing whorls, entirely exposed in the very 
wide, shallow umbilicus; sides flattened, very slightly convex, with an abrupt, nearly vertical, narrow slope at 
the edge of the umbilicus; periphery as broad as the mouth at edge of umbilicus, evenly rounded, very convex ; 
surface unknown; septa rather distant; mid-lobe large, very acutely angular, simply pointed, nearly as wide 
