666 CAMBKIAN BEACHIOPODA. 



The Missouri specimens were at first thouglit to be a distinct species, to wliich the name 

 L. hroadheadi was given, but the description was not published. By oversight the name 

 L. hroadheadi was pubhshed [Walcott, 1902, p. 601] in the preliminary notes on the genus. 

 Tlie valves of L. minuta almost cover a fragment of sandy shale from the Eureka district, 

 Nevada. Linnarssonella tennesseensis is fairly abundant in sandy shales and thin-bedded sand- 

 stones, also in argillaceous shales above the sandstone of the Rome formation. Three 

 species occur in tlie Upper Cambrian of the House Range section of western Utah. The lowest 

 in the section is L. transversa; about 200 feet higher in the section, L. modesta; and a short 

 distance above, L. ■ nitens. These species occur in abundance in the bluish-gray limestones. 

 Linnarssonella urania is moderately abundant in the Middle Cambrian, compact, dove-colored 

 limestones of the Wasatch Range. 



Failing to establish a satisfactory genus in honor of Linnarsson in the first instance," I 

 make another attempt with this rare and interesting form. 



A_ Linnarssonella girtyi Walcott. 



Plate LXXVIII, figures 5, 5a; Plate LXXIX, figures 1, la-r. 



Linnarssonella hroadheadi Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 601. (Name referred to but not defined 



or described. &) 

 Linnarssonella girtyi Walcott, 1902, idem, pp. 602-603. (Described and discussed as below as a new species.) 



Shell minute. General form broad ovate to subcircular. Ventral valve convex; beak 

 small and slightly incurved over the false area; false area short and varj^mg from vertical to 

 a backward inclination of 45° to 50° with the plane of the edge of the valve; in some examples 

 the margin of the false area arches (PI. LXXIX, fig. la') but in others it appears to be straight 

 (fig. lb). A very slightly indicated pseudodeltidium occurs beneath the beak that gradually 

 widens to the margin, very much as in Micromitra fealei. Pedicle opening minute exteriorly, 

 but the tube increases in size toward the inner surface of the shell. In one very perfect shell 

 the aperture appears to open into a narrow elongate depression just in front of the beak, but 

 it usually is seen as a minute, circular perforation at the apex of the beak. Dorsal valve 

 gently convex, with a minute beak at the posterior margin. Surface of the shell glossy and 

 smooth to the unaided eye, but a strong magnifier shows very fine concentric striae and lines 

 of growth; the inner surface is marked outside of the visceral area by very fine radiating striae. 

 The shell is formed of several layers or lamellae, and, judging from the depth of the impressions 

 of the muscle scars and vascular markings, rather tliick over the central and posterior por- 

 tions. The average length of the ventral valve is 1.5 to 1.75 mm.; the dorsal valve is slightly 

 shorter. 



The cast of the interior of the ventral valve shows the presence of a large cardinal scar 

 on each side of the visceral area, and outside of the very strong vascular canal; they are oval 

 in outline and probably the point of attachment of a strong muscle or muscles; their variation 

 in size and position is shown by Plate LXXIX, figures Ik and Im-p. The visceral area is 

 small, but is well defined in Plate LXXIX, figures In, lo, and Ip. Of the vascular canals only the 

 main trunks are shown by strong lidges in the casts, their form and extension being finely exhibited 

 by figures Im to Ip; in figure Ik they extend almost in a direct line from the beak to the 

 anterolateral margins of the valve. The cast of the interior of the pedicle tube is usually 

 broken ofi^; its position is shown in Plate LXXIX, figure In. The mterior of the dorsal valve 

 is beautifully shown by figure 1 1 ; the strong cardinal area with its well-defined pseudodeltidium, 

 the large oval cardinal scars immediately in front of the area, and the strong vascular canals 

 are as clearly defined as in the large shells of Oholus. The cardinal scars are divided into three 

 parts by two transverse lines crossing the outer slope more or less obliquely, but the divisions 

 on the two sides are unequal; the inner slopes of the scars are finely pohshed and afl'ord no 

 evidence of the attachment of muscles. Traces of the central scars occur on the outer slope 



o Linnarssonia [Walcott, 1885, p. 115], now referred to AcToiTd%. 



i Under the impression that the foims were distinct this name was given to them, and the name was overloolied when the description of the 

 genus was published (Walcott, 1902, p. 601]. 



