582 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxv. 



The cast of the- interior of the brachial valve shows a strong- median 

 ridge of variable length and size, large cardinal scars, and well-defined 

 central scars. 



Ohservations. — This species belongs with the series represented by 

 A. saglttalis and its varieties, and if uncompressed, nondistorted, well- 

 preserved specimens could be obtained, it is quite possible that it would 

 prove to be identical svith A. sagittalis transversa. Dr. Matth(>w thinks 

 it had a thinner shell; but that is not probable, as the apical callosity 

 and cardinal scars of the pedicle valve, and the median ridge, cardinal 

 and central scars of the brachial valve all indicate a shell quite as thick 

 as that of ^4. sagittal !s and varieties. 



Dr. G. F. Matthew kindly sent me the type and study material of 

 this species from his private collection. 



Formation and locality. — Middle Cambrian, Long Reach, Kings 

 County, New Brunswick. 



ACROTRETA BISECTA Matthew. 



Ac.-otreta baileyi Matthew?, Trans. Roy. Soc. C!aiiada, IX, 1892, p. 43, pi. xii, 



fig. 7d. 

 Acrotreta hisecia Matthew, Bull. Nat. Hist. Soc. New Brunswick, IV, 1900, p. 27o, 



pi. V, figs. 5a-g; IV, Pt. 5, 1902, p. 394, pi. xvi, figs. 2, 2a-g. . 



Nearly all the pedicle valves of this species are more or less com- 

 pressed in the shale, thus decreasing- the true elevation, Mr. Matthew 

 illustrates a pointed high pedicle valve, but does not sa}^ whether the 

 figure is diagrammatic. Some of the casts in the shale indicate a 

 sharply conical pedicle valve. When the apex is broken off, the cast 

 of a medium apical callosit}' is seen, with the base of the cast of a 

 medium-sized pyramidal tube; the cardinal scars are small and nearl}' 

 concealed by the cast of the strong main vascular sinuses. There is 

 considerable range of variation in the size and length of the median 

 ridge of the brachial valve. One specimen shows a strong- median 

 ridge, cardinal and central scars, and deeply excavated false deltidium. 



Surface marked by fine concentric stria? and lines of growth and very 

 fine undulating stria? that give the concentric stria? a fretted appear^ 

 ance when examined with a strong lens. 



The most nearly related species appears to be A. saT/riaa^ of the 

 Shineton shales. 



Formation and locaIitf/.—'Up\')er Cambrian, Barrachois Glen, -t miles 

 south of Little Bras D'Or Lake. Mr. Matthew's types came from 

 McLeod Brook, Cape Breton, Nova Scotia, and he also identifies it 

 from Div. C, 3c, at Navy Island, St. John Harbor, New Brunswick. 

 Mr. S. Ward Loper found many specimens of several horizons in the 

 shales on both sides of Barrachois River, near the Boisdale road, and 

 for some distance north; also on the east branch of the Barrachois 

 River, ('ape Breton, Nova Scotia. 



