GAsTERopopA. | LOWER PALZEOZOIC MOLLUSCA. 297 
TROCHUS HELICITES (Soi.) 
Ref —Sil. Syst. t. 3. f. le and 5. 
Sp. Ch.—Discoid, depressed ; apical angle 130°; spire of four gradually increasing whorls, slightly convex 
above, with simple impressed sutures; circumference obtusely rounded; base gently convex, with a small 
umbilicus; mouth wider than high, transversely oval; surface of the whorls nearly smooth, crossed by fine, 
slightly oblique strize of growth ; width eight lines, proportional height %, height of last whorl 3. 
Internal casts have the volutions more convex. 
Position and Locality —Common in the tilestone of Storm Hill, Llandeilo, Caermarthenshire; one 
specimen in the Bala limestone of Llandeilo, Caermarthenshire ; and a cast, apparently identical, in the Bala 
sandstone of Dalquorhan, near Girvan, Ayrshire. 
Trocuus Moore1 (M/°Coy). PI. 1. L. fig. 18. 
Ref—Id. M°Coy, Amn. Nat. Hist. 2nd Series, Vol. VII. p. 50. 
Sp. Ch.—Acutely conical ; apical angle 50°; of about five (four preserved) flattened, gradually increasing 
whorls; mouth transversely subquadrate ; base flattened, moderately convex ; umbilicus deep, narrow; surface 
unknown. Length about eight lines, proportional width 4, length of mouth #4, width of mouth 4, width 
of umbilicus 3. 
I dedicate this very distinct species to J. Carrick Moore, Esq., Secretary of the Geological Society, 
who has devoted much labour to the elucidation of the older fossiliferous rocks of Scotland. 
Position and Locality.—In the fine Bala sandstone of Dalquorhan, near Girvan, Ayrshire. 
Explanation of Figwres.—PI. 1. L. fig. 18, natural size; fig. 18 a, back view. 
Genus. EUOMPHALUS (Sow.) as here restricted. 
Gen. Char.—Shell discoid, spire flattened or slightly elevated, of numerous, usually angulated whorls ; 
umbilicus very wide, exposing the volutions; mouth with a nearly circular entire peritreme, not indented by 
the preceding whorl; surface usually sculptured. 
All the typical species of Sowerby’s genus Huomphalus (E. pentangulatus, catillus, &c.) belong unfor- 
tunately to the genus Straparollus of Montfort (as M. d’Orbigny has remarked), in which the mouth is 
incomplete on the left side, and is indented by the penultimate whorl: as however such species as his L. 
rugosus, EF. discors, &c. differ in having an entire peritreme, and often thickened nearly circular lip, as in 
Delphinula, 1 have thought it desirable rather than let the name Huomphalus drop out of use, to restrict it 
to the group of very distinct shells agreeing with the latter types; the genus as thus restricted being 
apparently intermediate between Delphinula and Turbo. The types first mentioned must of course be placed 
in De Montfort’s genus. 
EvoMPHALUS CENTRIFUGUS (Wahl. Sp.) 
Ref. and Syn. = Turbinites centrifugus Wahl. = Euom. substriatus, 2. centrifugus, and Inachus sulcatus 
His. Leth. Suec. t. 12. f. 1. 
Sp. Ch.—Discoid, of three to four gradually increasing volutions, which are completely exposed on both 
sides; spire depressed a little below the level of the body whorl; whorls very convex above, back obtusely 
rounded; a thick, flattened, plate-like keel extends horizontally from the circumference on a level with the 
lower edge; its width rather less than half the width of the whorl; upper surface of whorls, with strong, 
subequal, spiral sulci, nearly one line apart; under surface and keel crossed by fine, slightly oblique, lines 
of growth. Diameter (exclusive of keel) two inches three lines, proportional diameter of last whorl %, height of 
ditto =. 
[rasc. u1.] Qe 
