213 



Size. Length of the ventral (of M. refulgent] 9 mm. ; width, 11 mm.; 

 length of dorsal nearly 9 mm. 



Horizon and locality. In the fine dark gray shales of Band C. 3 c., at 

 McLeod brook, Boisdale, N.S. Common. 



Comparing the species with M. plumbea, there is a considerable differ- Cornered 

 ence in size, Salter's figures being of the natural size. Davidson's figures 

 show a shell about as large as the largest of M. refulgens. The proportion 

 of the outline of the valves given by Salter of 3 to 4 are different from 

 our species in which the proportion is about 5 to 6 ; the Cambrian species 

 therefore is rounder than the Ordovician. But Davidson's figure has nearly 

 the same proportion as the Cape Breton form. In Salter's species the 

 cardinal area of the ventral valve is higher, and the visceral cavity pro- 

 proportionately larger than in this species. 



Salter records a variety of M. plumbea ( plicata, Hicks) as occurring 

 in the Tremadoc group,* which would come almost within the range of 

 M. refulgens ; and forms like the latter have heen seen as low down as 

 the Assise a of Division 3 of the St. John Terrane. 



ORTHIS. 

 ORTHIS LENTICULARIS, Dalman, PL XVII, figs. 1 a~d. 



1821. Atrypa lenticularis WahL, Petr. Tell. Suec., p. 66. 



1827. Atrypa lenticularis Dalm., Vet. Acad. Handl. p. 132; Hist. Leth. 



Suec., p. 76. 

 1834. Spirifer ? lenticularis L. von. Buch., Abhandl. d. Berl. Acad. p. 48 



Tab. i, figs. 13-14. 

 1857. ) Atrypa lenticularis. Kjerulf., Geol. d. Siidl. Norw. p. 284. ; Vei- 



1865. j viser &c. p. 1-3, fig. 7. 



1866. Orthis lenticularis Dav., Geo. Mag. vol. v. tab. xvi, figs. 20-22. 

 1871. Orthis lenticularis Dav., Brit. Silur, Brach. p. 230, tab. xxxiii, 



figs. 22-28. 



1891. Orthis lenticularis. WahL, Trans. Roy. Soc. Can. vol. ix, sec. iv, 

 p. 48, pi. xii, figs. 9 a-d. 



The following is Wahlenberg's original description of this species : Orthis 

 Suborbicular, on each side a little convex, radially undulate. In a 

 "suillous" rock [fetid limestone] in beds of aluminiferous slate, in 

 which material no other shell has been found. It occurs plentifully every- 

 where throughout several provinces. In size and in its situation resem- 

 bles at first sight the pea-shaped entomostracan [Agnostus pisiformis] 



* Mem. Geol. Surv., G. Britain, vol. iii, pp. 355, 368. 



