TEMNODISCUS. 47 



LocaJiti/. — Thraive Glen, near Girvan. 



Remnrks. — The foregoing description is thai given by Ulrich and Scofield for 

 G. fimhriata, and it appears to apply very closely to a Girvan specimen in Mrs. 

 Gray's collection of which only the impression of part of the outer whorl is 

 preserved. The shell must have measured about 15 mm. in height (/. e. diameter), 

 and the outer whorl, which was subcordate in transverse section, rather higher than 

 wide, increases rather rapidly in size towards the mouth, and is crossed by 

 transverse undulated projecting lamellge, rather oblique to the whorl and set 

 at equal distances apart ; the fimbriations are 7-8 in number and form minute 

 rounded saddles and lobes, while in the interspaces between the lamellce are 

 delicate transverse concentric lines. 



Genus TEMNODISCUS, Koken. 



Generic Characters. — " Symmetrically involute small thin shells consisting of 

 one and a-half or two rapidly enlarging, contiguous or free volutions, with 

 rounded sides and a more or less well-developed slit-band ; aperture higher than 

 wide, sinuate dorsally, and somewhat deeply emarginated in front of the slit-band ; 

 marks of growth curving strongly backward, more or less distinctly lamellose, 

 with crenulated edges, and, when distant enough, traversed by small longi- 

 tudinal riblets " (Ulrich and Scofield). 



In 1896 Koken^ gave this name to a genus of Bellerophontacea with the type 

 species, Gyrtolitcs lamellifer, Lindstrom," but he had already, in 1889^ grouped this 

 species with four others, C. pharetra, G. arrosus, C. ohliquus and G. euryom.plialns, 

 as a subgenus of Gijrtolites, though without defining it by a name. Ulrich and 

 Scofield in 1897* chose the same species as the type of their genus Gyrtolitiiui, 

 being apparently in ignorance of Koken's earlier name, Temnodiscus. We must, by 

 the rules of priority, use Koken's designation for this group of Silurian shells. But 

 subsequently Koken,^ in 1897, in describing certain Ordovician shells under this name 

 gave a fresh definition of its characters, in which he stated that it had no slit-band, 

 whereas Ulrich and Scofield distinctly state that there is a "more or less well 

 developed slit-band," such as Lindstrom clearly describes and figures in the type 

 species. The American authors, moreover, do not include Lindstrom's G. eury- 

 oniphalus in their genus, but only G. lamellifer, G. pharetra, G. arrosus Siwd G. ohliquus. 

 Further, they say that in America the European genus Gyrtolitina is only repre- 



1 Koken, ' Die Leitfossilien ' (1896), p. 100. 



2 Lindstrom, ' Silur. Gastrop. Pterop. Gotland,' p. 82, pi. vi, figs. 31—38. 

 . 3 Koken, ' Neues Jahrb. f. Miner.' suppl. vol. vi (1889), p. 393. 



* Ulrich and Scofield, op. cit., p. 847. 



5 Koken, 'Gastrop. Bait. Untersilurs ' (1897), p. 129. 



