538 BRITISH PALAXOZOIC FOSSILS. [GasrERopopa. 
keels, the under or left one of greatest diameter, so that the periphery slopes slightly forwards and outwards, 
being very convex in the middle, becoming concave near the bounding keel on each side; umbilicus not bounded 
by the lower keel, but by the narrow, steep, inner edge of the flattened body-whorl, exposing all the turns of the 
spire; mouth subquadrate or trapezoidal from the slight convergence of the upper and lower edges, Surface 
crossed by rather strong, minute, transverse lines of growth. Average diameter five or six lines, proportional 
diameter of last whorl ;*), height of do. , width of umbilicus ;;. 
As this species grows large, for instance eight or nine lines in diameter, the whorls become more nearly 
trigonal in section, from the under side sloping rather more to the umbilicus than in the more ordinary speci- 
mens, making some approach to Straparollus catillus, in appearance, or to S. calyx, on a very small scale ; but it 
is distinguished from the young of the former by the greatest width being across the edges of the lower keel, and 
from the latter it differs in its greater depression or less height of the body-whorl. 
Position and Locality—Rare in the black carboniferous limestone of Derbyshire. 
STRAPAROLLUS? CATILLUS (Mart. Sp.) 
Ref. and Syn. = Helicites catillus Martin, Pet. Derb. t. 7. f. 1 and 2.= Huomphalus id. Sow. Min. Con. 
t. 45. f. 3 and 4, 
Dese.—Discoid, depressed, of five to six whorls, spire sunk considerably below the level of last roe 
periphery very convex a little below the middle, becoming slightly concave near the two strong, nearly equal, 
narrow, prominent, bounding ridges; umbilicus very wide, the sutures nearly coinciding with the bounding keel 
of the spiral turns; surface within the keel very slightly convex; surface from the upper keel sloping rapidly 
with slight concavity to the simple sutures; keel rather outside the middle on the spiral whorls; mouth sub- 
trigonal, upper and lower edges nearly equal. Diameter about one inch six lines, proportional width of 
80 
umbilicus from bounding ridge ;, diameter across upper ridge ,;, width of last whorl 33, of penultimate 
whorl ;;;, depth of mouth ;. Surface crossed by slightly sigmoidal, slightly oblique, lines of growth, obscurely 
decussated on the periphery, and within the edge of the umbilicus by obsolete spiral strize. 
This species is intermediate between S. calyx and NS. pentangulatus ; it differs from S. calyx in the less 
height of the body-whorl, and in the greater convexity of the periphery, and the keel forming the edge of the 
umbilicus being considerably less than the greatest diameter of the shell, while from the S. pentangulatus it 
differs in the sharp angular ridge bounding the umbilicus, being at least as marked as that on the upper side. 
Position and Locality.—Rare in the lower carboniferous limestone of Kendal, Westmoreland, and Lowick, 
Northumberland. 
STRAPAROLLUS COSTELLATUS (M/'Coy). Pl. 3. H. fig. 3. 
Ref—M°Coy, Ann. Nat. Hist. 2nd Series, Vol. XII. 
Desc.—Discoidal, depressed, very obtusely conic ; spire of rather more than six very gradually increasing 
whorls, each slightly convex above, strongly indenting the suture, which is an impressed sharp line ; apical 
angle 110° (from the obtuseness of the apex its angle would be larger in very young specimens) ; umbilicus 
very wide, rounded, half exposing all the whorls; base of body-whorl very convex, rounded, with a very obscure 
angulation at the edge of the umbilicus; periphery narrowed, obtusely rounded; upper surface of the whorls 
marked with sharp, slightly sigmoid, rather unequal ridges, arched obliquely backwards, becoming abruptly very 
much finer and more numerous on passing the circumference to the base (ten of the upper ridges in two lines 
on the body-whorl), each separated, by a sulcus, about its own diameter from the next. Diameter ten lines, 
proportional height of spire =, height of last whorl 4, distance between last and penultimate suture /°, width of 
60 
umbilicus ©, width of mouth “ 
This species is distinguished from its congeners by the beautifully sharp costellation, or transverse sculp- 
turing of the whorls of the spire, which abruptly ceases on the base of the body-whorl, or becomes there con- 
founded with the lines of growth. The inner lip is complete, but thin, as in other species of Straparollus, 
distinguishing them from Platyschisma. 
