ZONIDISCUS GRAYI. 71 



Whorls five, transverse, carinatecl on the dorsal side. Umbilicus open and large 

 with steep borders. The transversal striae of the surface crowded; joining the slit- 

 band in an acute angle of 32°, they are bent outwards and backwards to the 

 umbilicus. In several specimens there is an indistinct carina on both sides of the 

 slit-band and parallel to it, placed at the point where the transverse striae are 

 bending backwards. The slit-band is elevated, flat on its top, finely and transversely 

 sculptured, somewhat concave along its median line and bordered on each side by 

 two thin-edged lines" (Lindstrom). 



Horizon. — Lower Ludlow. 



Locality. — Vinnal Hill. 



Uemarlcs. — The poorly preserved examples of this species of Cymbularia which 

 are in the Jermyn Street Museum [28095, 2809G, 28093, 280941 and come from 

 the Lower Ludlow of Vinnal Hill, may be compared with Lindstrom's species 

 II. fastigiatus, the description of which as given by him is above quoted. The 

 enrolment of the whorls, shape of the dorsum, carination, size of the umbilicus, 

 dorsal sinus and ornamentation seem to agree most closely with that species. 



Genus ZONIDISCUS, Spitz. 



Generic Characters. — Shell compressed, sharply carinated ; umbilicus open. 

 Whorls higher than wide, more or less lanceolate in cross-section ; dorsal lip with 

 long narrow median slit followed by narrow slit-band ; inner lip reflexed. 



This genus was founded in 1907 by Spitz 1 for a group of compressed shells 

 with sharp dorsal edge and slit-band and the habit of Oxydiscus. Cyrtolites discus, 

 Lindstrom, 2 from the Silurian of Gotland, was chosen as the type, and a Lower 

 Devonian species, O.vydiscus geyeri, Freeh, 8 was also given as an example of the 

 genus. Spitz (op. cit.) moreover referred Ulrich and Scofield's Oxydiscus cristatus, 

 Safford, and Lindstrom's Cyrtolites euryomphalus to it. 



Koken's Temnodiscus (==. Cyrtolitina, Ulrich and Scofield 4 ) may probably be an 

 allied genus, but it has a different surface-sculpture, a less compressed lenticular 

 shape and a less carinate dorsum. 



1. Zonidiscus grayi, sp. nov. Plate XI, figs. 13—15. 



Specific Characters. — Shell compressed, lenticular, thickest at umbilical edge, 



dorsally acute, composed of 3 — -i whorls. Whorls high, narrow, lanceolate in 



cross-section, bearing elevated compressed prominent carina ; sides gently convex, 



' Spitz, " Gastrop. Karuischen Unterdevon," 'Beitr. Pal. G-eol. Oesterr. u. Orients,' vol. xx (1907), 

 p. 124, pi. xi (i), fig. 7 a — c. 



- Lindstrom, ' Silur. Gastrop. Pterop. Gotland,' p. 84, pi. vii, figs. 18 — 21. 



3 Freeh, ' Zeitschr. deutsch. geol. Gesell.,' vol. xlvi (1894), p. 463, pi. xxxiv, fig. 2. 



4 Ulrich and Scofield, op. cit., pp. 847, 866. 



