ACROTRETID^. 



671 



Pedicle opening situated on the umbo a short distance above the point of the beak; on some 

 shells it opens on the plane of the surface of the valve, and on others it has a rounded, shghtly 

 elevated margin. Dorsal valve slightly convex, with a minute beak at the posterior margin. 

 Surface of the shell glossy, with very fine concentric strise and Unes of growth. A ventral valve 

 2.5 mm. in length has a width of 1.75 mm. The dorsal valves are somewhat shorter in propor- 

 tion to the width. 



A partial cast of the interior of the ventral valve shows a small visceral area in front of the 

 pedicle 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. 



Observations. — This species differs from L. girtyi Walcott in not having a false area in the 

 ventral valve, and also in the position of the pedicle opening. The incurved apex is more hke 

 L. modesta, but the form of the ventral valve and the position of the pedicle aperture are quite 

 different. 



Formation, AND locality. — Middle Cambrian: (55u) Limestones about 200 feet (61 m.) above the Lower Cam- 

 brian [see Walcott, 1908f, p. 171], 0.25 mile (0.4 km.) below the Maxfield mine, in Big Cottonwood Canyon, on the 

 west front of the Wasatch Mountains, southeast of Salt Lake City, Salt Lake County, Utah. 



Genus ACROTRETA Kutorga.o 



{Siipoc, at the top; and T/»)T(Sf, bored through.] 



Acrotreta Kutorga, 1848, Verhandl. Russ.-kais. min. Gesell. St. Petersburg for 1847, No. 12, pp. 259 and 260 (notes 

 on genus), and p. 275 (described in German as a new genus; see p. 672 for translation). 



Acrotreta Kutorga, Morris, 1849, Annals and Mag. Nat. Hist., 2d ser., vol. 4, pp. 316 and 318. (Characterized and 

 discussed.) 



Acrotreta Kutorga, Davidson, 1853, British Fossil Brachiopoda, vol. 1, Introduction, No. 3, p. 133. (Described and 

 discussed as a possible subgenus.) 



" The synonymy for this genus does not give a complete record of the various genera under which the species now included in Acrotreta were 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record the following mere generic 

 references are hsted: 



Discina Shumard [1861, p. 221]. 



Acrotreta Billings [1805a, p. 216]. 



Ololella, Salter [1866, p. 285]. 



Discina Salter [1866, p. 285]. 



Obolella Hartt [1868, p. 644]. 



Lingula Barrande [1868a, p. 102; 1868b, p. 692]. 



Obolella Davidson [1868, pp. 309 and 310]. 



Acrotreta? Davidson (1868, p. 314]. 



Obolella Davidson [1871, pp. 339 and 340]. 



Obolella? Billings [1872b, p. 470]. 



Acrotreta Meek [1873, p. 463]. 



Obolella ? Billings [1874, p. 69]. 



Metoptoma Callaway [1874. p. 196]. 



Acrotreta White [1874, p. 9]. 



Acrotreta Linnarsson [1876, p. 16]. 



Obolella Linnarsson [1876, p. 19]. 



Acrotreta Linnarsson [1877, p. 374]. 



Acrotreta White [1877, p. 53]. 



Obolella Callaway [1877, p. 669). 



Acrotreta Swanston [1877, PI. VII figs. 21a-c]. 



Obolella Hartt [1878, p. 644]. 



Obolella Linnarsson [1879, p. 27]. 



Obolus? Barrande [1879b, PI. XCV: ii]. 



Acrotreta Barrande [1879b, PI. XCV: vn). 



Acrotreta Brogger [1882, pp. 45 and 46]. 



Obolella Davidson [1883, p. 211]. 



Acrotreta Davidson [1883, p. 213]. 



Obolella Walcott [1884a, p. 16). 



Obolella ? Walcott [1884b, PI. I, fig. Ic]. 



Acrotreta Walcott [1886b, p. 98]. 



Lingulella f Matthew [1886, p. 33]. 



Acrotreta Matthew [1886, p. 36]. 



Acrotreta Swanston [1886, PI. VII, figs. 21a-cl. 



Linnarssonia Walcott [1887, p. 189]. 



Linrmrssonia Oehlert [1889, p. 1138). 



Linnarssonia Walcott [18S9b, p. 36]. 



Obolella Dawson [1888a, p. 55; 1888b, p. 55J. 



Acre/:''". Walcott [1889c, p. 441]. 



Linnarssonia Walcott [1889c, p. 442]. 



Obolella (Linnarssonia) Dawson [1890, p. 53]. 



Linnarssonia Hall [1890, p. 55]. 



Obolella Hartt [1891, p. 644]. 



Acrotreta Walcott [1891a, p. 608]. 



Linnarssonia Walcott [1891a, p. 610 and PI. 



LXVIII, flgs. 2a-dl. 

 Obolella Hall and Clarice [lS92c, p. 103]. 

 'Acrotreta Matthew [1892, p. 43; 1834, p. 87]. 

 Linnarssonia Matthew [1895a, p. 125]. 

 Acrotreta Matthew [1895a, p. 126]. 

 Lingulellaf Matthew [1895a, p. 127]. 

 Obolella WaUerius [1895, p. 65]. 

 Acrotreta Wallerius [1895, p. 66]. 

 Linnarssonia Matthew [1897, p. 169]. 

 Linnarssonia Schuchert [1897, p. 262]. 

 Linnarssonia Freeh [1897; PI. lA, figs. 3a and 3bJ. 

 Lingulellaf Matthew [1898a, p. 128]. 

 Acrotreta Walcott [1899, p. 449]. 

 Acrotreta Matthew (1901a, p. 275]. 

 Acrothyra f Matthew [1901b, p. 304]. 

 Acrotreta Matley [1902, p. 142). 

 Acrotreta? Matley (1902, p. 14.3]. 

 Acrotreta Matley [1902, p. 144]. 

 Linnarssonia Matley [1902, p. 145]. 

 Linffulella (Acrothyra ?) Matthew [1902b, p. 390]. 

 Acrothele Matthew (1902b, p. 404). 

 Acrotreta Matthew [1902c, p. 109). 

 Acrotreta Walcott [1902, pp. 580-600]. 

 Acrotreta Wiman [1902, pp. 54 and 55]. 

 Obolella Wiman (1902, p. 66], 

 Acrothele Matthew [1903, p. 103]. 

 Acrotreta Walcott [1905a, pp. 298-303J. 

 Acrotreta Moberg and Segerberg [1906, pp. 64, 65, 



and 66). 

 A crotreta Walcott [1908c, p. 245; 1908d, pp. 93, 94, 95, 



and 96]. 



