414 CAMBRIAN BRACHIOPODA. 



The parietal scar is clearly shown in front of the visceral cavity of the ventral valve, between 

 the main vascular sinuses (ps) (PL XXXVII, fig. Id), but it has not been traced beyond the 

 main sinus. On the dorsal valve its course may be followed from the median line in front of the 

 anterior lateral muscle scars (j), back beyond the central scars (h), to a point where it curves 

 outward (ps) (PL XXXVII, fig. Ic). 



Observations. — Matthew sent me the types of this species for study and illustration. From 

 the first lot sent in 1900 the figures on Plate XXXVII were made. A second lot sent in 1903 

 gave the fine illustrations on Plate XXXVI. The two figures in his paper (1895b, PL I) of the 

 ventral and dorsal valve are essentially diagrammatic, com-binmg as they do the characters seen 

 in a number of specunens. I have illustrated several of the specimens that appear to me to 

 give a fair presentation of the characters. 



As stated by Matthew [1895b, p. 256] the plan of the muscular scars of this species is very 

 nearly that of Obolus apollinis quenstedti (Mickwitz) . It may also be compared with the arrange- 

 ment of the scars of Lingulella acutangula (Roemer). Further reference to 0. selwyni will be 

 found under the discussion of Oholus and Lingulella (p. 377). In a general way comparison 

 may be made between Obolus selwyni and Lingulella acutangula; specifically there are strong 

 variations between them. 



Obolus sequiputeis Matthew appears to be in all respects identical with 0. selwyni. To 

 illustrate the identity of the two species photographs were made of the types of 0. se.guiputeis 

 (PL XXXVI, figs. 2, 2a-b). The dorsal interiors have both been distorted. In figure 2b the 

 distortion is from transverse compression; in figure 2c from longitudinal compression. The 

 specunen represented by the latter is associated with Obolus selwyni. The specimens represented 

 by Plate XXXVI, figures 2a and 2b, are casts in a matrix that preserves the interiors very 

 clearly. Plate XXXVI, figure 2c, and all other illustrated specimens of this species, are from 

 a matrbc in which the shell is compressed so as to obscure the interior markings. 



The calcareous sandstones in which this species occurs were referred to the Ordovician by 

 Matthew [1895b, p. 255], but in his review of the Cape Breton Cambrian faunas [1903, p. 123] 

 he assigns it to Division E2a ? of his lower Etcheminian. 



The specific name was given in honor of Dr. A. R. C. Selwyn. 



Formation and locality. — Middle Cambrian: (307d [Matthew, 1903, p. 123]) Sandy limestone of Division 

 E2a? of Matthew's [1903, p. 19] Etcheminian, on Young (McFees) Point near George Kiver Station, on the 

 Intercolonial Railway, eastern Cape Breton, Nova Scotia. 



Obolus septalis (Walcott). 



I 



Plate XXIII, figure 3d; Plate XXXIV, figures 2, 2a. 



Oholus {Lingulella) septalis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 331. (Characterized as below^ as a new 



species.) 

 Obolus mcconnelli Walcott (in part), 1908, Canadian Alpine Journal, vol. 1, No. 2, p. 244, PL I, fig. 2a (not fig. 2, which 

 represents a specimen of Obolus mcconnelli). (No text reference. Fig. 2a is copied in this monograph, PI. 

 XXIII, fig. 3d.) 



The dorsal valve is all that is known of this little shell. There are two specimens in the 

 collections of the United States National Museum and three in the collection of Bryon E. Walker, 

 of Toronto, Canada. 



The general form of the valves is much like that of Obolus rotundatus (Walcott) (PL XX). 

 It is distinguished from the latter and other described species by the strong median ridge and 

 septum of the dorsal valve. The outer surface is marked by concentric striae and fines of growth 

 and very fine irregular concentric striae that give a minutely rough surface. 



This form owes its specific name to the presence of a septum in the dorsal valve. 



Formation and locality. — Middle Cambrian: (14s) About 2,300 feet (701 m.) above the Lower Cambrian and 

 2,700 feet (823 m.) below the Upper Cambrian in the Ogygopsis zone of the Stephen formation [Walcott, 1908f , p. 210], 

 at the "fossil bed' ' on the northwest slope of Mount Stephen, above Field on the Canadian Pacific Railway, British 

 Columbia, Canada. 



