14 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



posterior extremity of the straight cardinal edge and constitutes the 

 upper one-fifth to one-third of the posterior margin. This short 

 dorso-posterior side is best defined in species in which the remainder 

 of the posterior outline trends somewhat forward, and manifestly 

 least distinct in species like B. robusta, in v/hich the backward trend 

 prevails also in the lower part of this portion of the outline. In a 

 few cases, notably B. acuta, and in a less degree B. benepuncta and 

 B. scrutator, the general outline in a side view of the valves conforms 

 to that of a right-angled triangle, the dorsal edge being the vertical, 

 the posterior the base, and the ventral side the hypothenuse. As a 

 rule the transverse diameter exceeds the vertical, in one case (a new 

 species for which the name B. elongata is suggested), the dimensions 

 being to each other about as 2 to 1. In the other extreme (likewise 

 represented by a new species for which the name B. curta is suggested) 

 the vertical diameter is considerably greater than the transverse. 



All of these variations in form, however, are closely knit together 

 by intermediate phases, and as no genetic departure from the generic 

 type maintained throughout the whole group seems to have been 

 established, a wholly satisfactory subgeneric grouping of the species 

 has so far failed to suggest itself. Still, it may prove that the fol- 

 lowing provisional arrangement of the species in sections is more 

 natural than we believe at present. 



1. Section of B. scrutator; 3. Section of B. perspicator : 



B. scrutator Matthew (genotype). B. perspicator (Matthew). 



B. oculata (Matthew). B. spectator Matthew. 



B. vigilans Matthew. B. spectator spinosa (Matthew). 



B. vigilans concenirica, new variety. B. curta, new species. 



B. benepuncta (Matthew). 4. Section of B. cambrica: 



B. bcnep uncta var. spissa, new ?B. obesa (Matthew). 



variety. ?B. concinna (Matthew). 



B. medialis, new species. B. cambrica (Matthew). 



B. acuta (Matthew). 5. Miscellaneous species: 



B. subquadrata, new name ( = B. Schmidtella pervetus Matthew. 



spectator acuta Matthew) . Bradoria minor Matthew. 



B. elongata, new species. Bradoria? steadi Matthew. 



2. Section of B. rugulosa: Bradoria primaeva (Matthew). 

 B. ovalis (Matthew). Bradoria aurora Matthew. 



B. rugulosa Matthew. Bradoria? ornata Matthew. 



B. robusta (Matthew). Bradoria fennicus (Wiman). 



B. robusta var. longula, new variety. Bradoria nitida (Wiman). 



B. tontoensis, new species. Bradoria hicksi Jones. 



BRADORIA SCRUTATOR Matthew 



Plate 1, Figures 11, 12; Plate 3, Figure 11 



Bradoria scrutator Matthew (part), Bull. Nat. Hist. Soc. New Brunswick, No. 

 18, 1899, p. 204, pi. 4, figs, la-lc; Canadian Record Sci., vol. 8, 1902, p. 451; 

 Geol. Surv. Canada, Rept. Cambrian Rocks Cape Breton, 1903, p. 163, pi. 

 13, figs, lo-lc. 



