92 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ^5 



LINNARSSONELLA TRANSVERSA, new species 



Plate 9, Figure 6 



This is a small shell that at first sight suggests L. iiwdcsta; it 

 differs from that species in the valves being more convex, transverse 

 instead of circular, and in having stronger concentric strise, and, in 

 some instances, radiating strise. A few fragments of the interior of 

 the dorsal valve indicate that the main vascular sinuses are well out 

 toward the outer margin, and that small circular depressions occur 

 on each side of the median line, very much as in the dorsal valve of 

 L. girtyi (Walcott) [1902, p. 602], and two small central muscle 

 scars midway between the posterior and anterior margins of the 

 valve. L. transversa differs from all other species of the genus 

 known by its transverse outline. The average shell has a width of 

 2 mm., w'ith a length of from 1.5 to 1.75 mm. 



Formation and Locality. — Upper Cambrian : At 930 feet 

 (283.5 """O above the Middle Cambrian and 2,385 feet (726.9 m. ;■ 

 below the top of the Upper Cambrian, in the arenaceous shales and 

 limestones of the Orr formation [Walcott, 1908a, p. 10], 4 miles 

 (6.44 km.") south of Marjum Pass, House Range, Millard Count}-, 

 Utah. 



LINNARSSONELLA URANIA, new specie 



Plate 9, Figures 9 and 9.7 



Shell minute, general form elongate oval. Ventral vaWe convex ; 

 apex minute and curved down nearh- to the plane of the margin of 

 the valve ; false area, if present, must be very narrow. Foraminal 

 opening situated on the umbo a short distance above the point of the 

 beak; on some shells it opens on the plane of the valve, and on 

 others it has a rounded, slightly elevated margin. Dorsal valve 

 slightly convex, with a minute beak at the posterior margin. Sur- 

 face of the .shell glossy, with very fine concentric striae and lines of 

 growth. A ventral valve 2.5 mm. in length has a width of 1.75 mm. 

 The dorsal valves are somewhat shorter in proportion to the width. 



A partial cast of the interior of the ventral valve shows a small 

 visceral area in front of the foraminal opening. The interior of the 

 dorsal valve is marked by a strong central ridge that extends from 

 the beak four-fifths of the distance to the front margin; on each side 

 of the median ridge, near the posterior margin, there is a rather 

 large, clearly defined cardinal muscle scar. 



Obser\'ATions. — This shell occurs in considerable numbers in a 

 cnmj^act. hard, dove-colored limestone Co to 75 feet (18.3 to 22.9 m.) 



