﻿Vol. 6 1.] THE SILTJEIAJSr KOCKS OF LLOrGADOCK. 573 



Family Trochonjbmatidjs, Ulrich. 

 Genus Gyronema, Ulrich. 1 



Diagnosis. — Whorls ventricose ; aperture moderately oblique ; 

 umbilicus small. Ornamentation consisting of spiral ridges, two 

 of which often form a more or less distinctly-marked peripheral 

 band, the ridges being most numerous on the base. 



Type. — Gyronema jpulchellum, Ulrich. 2 



Eemarks and Resemblances. — This genus was created for 

 the reception of shells intermediate in character between Trocho- 

 nema, Salter, and Oyclonema, Hall.. The open umbilicus, as well as 

 a vertical peripheral band, connects it with Troclionema. It is dis- 

 tinguished from that genus by the more elevated spire, less oblique 

 aperture, and also by the peripheral band not being quite so 

 distinctly marked, and there is frequently a submedian keel on it. 

 The elevated spire causes it to bear some resemblance to Oyclonema, 

 but it differs in having an open umbilicus. 



Gyronema Octavia (d'Orb.). (PI. XXXVII, figs. 10-15.) 



Turbo carinatus, J. de C. Sowerby, 1839, in Murchison's ' Silurian System ' p. 612 

 & pi. v, fig. 28; non Turbo carinatus, Sow. 'Mineral Conchology ' 1821, 

 pi. ccxl, fig. 3 ; non Turbo carinatus, Honinghaus, 1830, Jalirb. f. Min. Geol.& 

 Petrefkde. p. 230, which is identical with Helix carinatus, Sow. 'Min. Conch.' 

 1812, vol. i, p. 34 & pi. x. 



Turbo Octavia, A. d'Orbignj', 1850, ' Prodrome de Paleontologie stratigraphique ' 

 vol. i, p. 30. 



Cyclonema carinatum, G. Lindstrom, 1884, ' Silurian Gastropoda & Pteropoda of 

 Gotland ' Kongl. Svensk. Vet.-Akad. Handl. vol. xix, No. 6, p. 178 & pi. xviii r 

 figs. 28-30. 



Diagnosis. — Shell turbinate, acute, having about six whorls. 

 Whorls increasing somewhat rapidly, convex, ornamented by spiral 

 keels. The three or four upper keels are frequently stronger than 

 the others ; the grooves between them vary in width, and the third 

 groove generally forms a peripheral band. There are additional keels 

 on the body-whorl, which vary in number on different specimens, and 

 there is always a strong ridge round the umbilicus. The lines of 

 growth cross the keels rather obliquely, and some are so strong as 

 to be almost lamellar. Umbilicus open. Aperture subovate ; outer 

 lip thin and sharp ; inner lip reflected on the body-whorl, and 

 partly covering the umbilicus. 



Eemarks and Resemblances. — The type of Sowerby's Turbo 

 carinatus is stated to be from the Upper Ludlow of the Trewerne 

 Hills, but unfortunately I have been unable to trace its existence 

 anywhere. It is not in the Geological Society's Collection, nor in 

 the Museum of Practical Geology, London. I have enquired in 

 several other Museums, but without result. His description and 

 figure are hardly definite enough for a satisfactory comparison with 

 other shells. There are numerous specimens in Prof. Groom's 



1 Final Eep. Geol. & Nat. Hist. Surv. Minnesota, vol. iii, pt. ii (1897) 

 p. 1046. 



2 Ibid. p. 1054 & pi. lxxviii, figs. 19-21. 



