N0.1299. CAMBRIAN BRACHIOPODA—WALCOTT. 597 



primseva occurs in the upper zone of the Olenellus fauna in Nevada, 

 and this is in the upper portion of the same fauna in the Appalachian 

 region. Its association with Microd'mcus connexas, a representative of 

 Jflcrodiscus punetatus, of the Pamdoxides zone of New Brunswick, 

 also serves to connect it with Acrotreta saglttalis. It appears to be 

 one of the few forms that serve to connect the Cambrian fauna of the 

 Atlantic province wath that of the Appalachian province. 



Fnnnation and localities. — Upper portion of Lower Cambrian. 

 Limestone interbedded in shaly slates. Rock Hill schoolhouse. near 

 North Greenwich; Ih miles east, also west of North Greenwich: west 

 summit of Bald Mountain, in the town of Greenwich; 2 miles south of 

 North Granville; on the roadside just west of Low Hampton crossing 

 of the Poultney River; one mile south of Shushan, one mile east of 

 Salem, northeast section of Whitehall Township on SSW. road from 

 Low Hampton — all in Washington County; Schodack Landing. Kin- 

 derhook Creek below paper mill at Stockport, Rensselaer County; 

 near Yalatie Creek near line of Nassau and Schodack townships, 

 Columbia County, New York. 



ACROTRETA SCHMALENSEI, new species. 



Acrotreta sodalis Lixnarssox, Brach. Paradoxides Beds of Sweden. Bihansr till 

 K. Svenska vet akad. Haudl., Ill, 1876, No. 12, p. 16, pi. in, figs. 32-.S.1.— 

 Wallerius, Undersokningar ofver zonen med Agnostus Isevigatvs i Vestergot- 

 land. Akad. Afhandl. Lund, 1895, p. 66. 



As in the case of many other species of this genus, the student is 

 referred to the series of figures illustrating it for information as to the 

 external outline, form, and convexit}' of the two valves and the range 

 of known variation. The collections of the U. S. National Museum 

 contain a large series of specimens, from which the shells illustrated 

 were selected. 



The broad false area has a shallow, faint median groove on some 

 specimens, and on others no traces of it have been seen. The foram- 

 inal aperture, which is exceedingly minute, is situated at the extreme 

 apex of the pedicle valve; the cast of the base of the foraminal tube is 

 clearly shown in interior casts of the valve. One of the distinguish- 

 ing characters is the cast of the large main vascular sinuses on each 

 side -of the visceral area. The casts of the interior of the brachial 

 valve are interesting and instructive in showing the considerable vari- 

 ation in the size and length of the median ridge and the size of the 

 cardinal and central scars. 



The shell is small and is built up of a thin outer layer and several 

 inner layers as lamellae more or less oblique to the outer layer. The 

 outer surface is marked b}- fine concentric strite and lines of growth, 

 and the inner surfaces of the lamellae by concentric striae and fine radi- 

 ating stri». The average length of the opening of the valves is 1.5 to 

 2 mm., and the width is usuallv a little more. 



