NO- i^w"^- CA MBL'L [ X nh'A ('HIOPODA— WA LCO TT. 251 



ventral valve occurs, specimens of the ventral valve from Bic show a 

 shorter deltidium than is usually present. 



A num]>er of exfoliated shells occur in the collection from the dark 

 ^n-ay compact limestone of eastern New York that are womewhat 

 douhtfully referred to this species. 



\ii<H!:<la festhiata is a strongly marked species that appears to have 

 hut one near representative in N. {Jautesella) perjMsta. The latter 

 (litters in the absence of spines and form of the ventral valve. 



Formation and locality. — Lower Cambrian. Upper portion of 

 Olenellus zone, Georgia formation. In limestone 'Mentile" a))out 2 

 miles east of Swan ton; in silico-argillaceous shales, with Olenellus 

 thomjysoni, Parker's quarry, town of Georgia; and in arenaceous 

 magnesian limestone about 2 miles east of Highgate Springs, Franklin 

 County, Vermont. Also in dark gray limestone interbedded in silic 

 eous shales 2 miles south of Middle Granville, Washington County, 

 New York. 



In limestone bowlder of the conglomerate on the east side of the 

 entrance to Bic Harbor. Province of Quebec. Fragments of Olenelhis 

 and Mlcrodiscus occurred in association with A\ festinata in the lime- 

 stone bowlders. 



Emigsville limestone, on left })ank of Codorus Creek, below Meyers 

 Mill, near Emigsville, 4 miles from York, Pennsylvania. 



NISUSIA FESTINATA TRANSVERSA Walcott. 



Orthisina ? transversa Walcott, Bull. U. S. Geol. Sur. No. 30, 1886, p. 121, pi. vii, 

 figa. 5, 5a. 



Original description. — Shell small, transversely eubquadrangular in outline, front 

 broadly rounded, angle formed by the union of the cardinal slopes of the ventral 

 valve 155° to 165°, hinge line straight and as long as the width of the shell. Area of 

 the ventral valve of moderate height, bent back from the hinge line, divided by a 

 triangular foramen that is higher than wide, and covered by a convex deltidium; the 

 area of the dorsal valve is bent back at more than aright angle to the hinge line; 

 foramen higher than wide, covered by a deltidium. 



Surface marked by numerous radiating, fine, even costse, eight in a distance of 

 3 mm., on the frontal margin of the ventral valve; a few concentric lines of growth 

 cross the radiating c'ostae, but not so as to give them a nodose character. 



Interior characters unknown. The fine radiating strias and transverse form dis- 

 tinguish this from other described species known to me. 



Since 1886 I have obtained a much larger series of specimens, and 

 do not think that this form should be considered more' than a variety- 

 of iV. festinata. 



Formation and locality. — Lowei' Cambrian, Georgia formation. 

 Silico-argillaceous shales of Parker's quarry, town of Georgia, Frank- 

 lin County, Vermont. 



