SINUITES ELONGATUS. 



5. Sinuites discoides, sp. nov. Plato I, figs. 9 — IJ. 



Sjjecific Characters. — Shell niucli compressed laterally, lenticular ; outer whorl 

 almost completely enveloping inner whorls and very rapidly increasing in height ; 

 umbilicus very small, nearly closed, situated at about one-third the height of shell ; 

 umbilical edge angular to subangular. Outer whorl with very gently convex or 

 flattened sides ; dorsum sharp, acute, except near mouth, where it l)ecomes 

 narrowly rounded. Mouth high, narrow, not expanded laterally, widest at base, 

 about twice as high as wide, with deep, narrow, acutely V-shaped sinus in upper 

 lip and large projecting subparallel angular apertural lobes, their inner and outer 

 edges meeting at about 75°; base of lips slightly reflected over umbilicus. 

 Surface of shell covered with very fine transverse strice bending back to meet 

 the sharp dorsal edge at about 30° or less, with very delicate revolving lines 

 decussating them on sides of whorl. Interior with one or two short rounded 

 submarginal thickenings behind sinus on dorsum dying out on sides. 



Dimensions. — i ii 



Height of shell ..... 15 . 13 mm. 



Height of outer whorl above umbilicus 10 . 9 ,, 



Horizon. — Lower Ordovician : Balclatchie Group. 



Localities. — Balclatchie ; Ardmillan ; Dow Hill. 



BemarJiS. — This shell must be referred to the genus Sinnites, in spite of its 

 compressed shape and sharp dorsal edge. The apertural lobes, the small or 

 closed umbilicus, the internal ridges, and the embracing whorls indicate its affinities. 

 The revolving lines are rarely visible, but the ornament on the whole reminds us 

 of (8. cri/pficus. If the umbilicus were open and larger, and the whorls only just 

 in contact, we might consider its reference should be to Temnodiscus, Perner. 

 The shell is thin and corneous in appearance, like that of S. balclatchiensis. 



There are two specimens [28100, 28101] in the Jermyn Street Museum from 

 the Arenig of White Grit Mine, Shelve, which may be doubtfully referred to this 

 species. They show the general characters and fine revolving lineation of 

 8. discoides, but are much crushed and distorted, so that their precise identification 

 is almost impossible. 



6. Sinuites elongatus (Portlock). Plate I, figs. 12 — 14. 



1843. Bellerophon elongatus, Portlock, Geol. Eep. Londond., p. 397, pi. xxix, figs. 4 a, 4 6. 



Specific Characters. — Shell somewhat compressed, outer whorl completely 

 embracing inner whorls. Umbilicus closed, situated at less than half height 

 of shell. Outer whorl very rapidly increasing in height to mouth, and much 

 less rapidly in width ; dorsum narrow, rounded. Mouth higher than wide, 



2 



