ACROTRETIDiE. 713 



the species with the material available for study, and I have entered it in this monograph as 

 Acrotreta sp. undt. (see p. 715). 



Formation and locality. — Middle Cambrian: (8z) Limestones of Paradoxides aelandicus zone, Borgholm, Oeland 

 Island; (320n) limestones of the Paradoxides forchhammeri zone at Lovened, Djupadal, 19 miles (30.6 km.) south-south- 

 east of Skara, Province of Skaraborg; and (8w) limestones of Paradoxides forchhammeri zone at Andrarum, 20 miles 

 (32.2 km.) northwest of Simrishamn, Province of Christianstad; all in Sweden. 



(334g [Seebach, 1865, pp. 340 and 34-l\) Limestones on Bornholm Island, Denmark. 



Acrotreta spinosa Walcott. 



Plate LXXIX, figures 4, 4a-a:. 



Acrotreta spinosa Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 302. (Characterized as below, as a new species.) 



The general form of this shell is much like that of Acrotreta idahoensis Walcott (PI. LXVIII, 

 figs. 2, 2a-g). It differs in having a straighter posterior margin. The distinguishing character 

 of the species is the spinose outer surface. The surface is marked by fine concentric lines of 

 growth at irregular intervals, with numerous, very fine, threadlike strise between. On some 

 shells occur radiating, more or less irregular, fine, rounded ridges that are formed by the 

 elevated elongate spine bases. Wlien these elongate bases are irregularly arranged the radiat- 

 ing ridges are not present. Owing to their minute size, the spinules are rarely seen. 



Formation and locality. — Upper Cambrian : (65) Limestone on east side of Sierra Canyon, opposite Pinnacle 

 Peak; (62a) limestone on east side of Sierra Canyon, opposite the Jackson mine; (62) limestone in the Dunderberg 

 shale [Walcott,' 1908f, p. 184], in canyon immediately north of Adams Hill; and (61) limestone in the Dunderberg shale 

 [Walcott, IBOSf, p. 184], a little south of the Hamburg mine; all in the Eureka district [Hague, 1892, Atlas], Eureka County, 

 Nevada. 



Acrotreta subconica Kutorga. 



Plate LXXIII, figures 2, 2a-i. 



Acrotreta subconica Kutorga [not Meek], 1848, Verhandl. Russ.-kais. min. Gesell. St. Petersburg for 1847, No. 12, 

 p. 275, PI. VII, figs. 7a-c. (Described in German as a new species; see below for translation. Figs. 7a, 7b, 7c, 

 7b', and 7c' are reproduced in this monograph, PI. LXXIII, figs. 2, 2a-d, respectively. The specimens repre- 

 sented by figs. 7a, 7b', and 7c' are redrawn in this monograph, PL LXXIII, figs. 2e, 2h, and 2i, respectively. 

 Figs. 2f and 2g on PL LXXIII of this monograph represent one of Kutorga's type specimens, but he figured 

 only the dorsal valve, 1848, PL VII, fig. 7c'.) 



Acrotreta Morris, 1849, Annals and Mag. Nat. Hist., 2d ser., vol. 4, PL VII, figs. 4a-b. (No text reference. Figs. 

 4a and 4b are copied from Kutorga's figures, 1848, PL VII, figs. 7b' and 7c', respectively, of Acrotreta subconica.) 



Acrotreta subconica Kutorga, Davidson, 1853, British Fossil Brachiopoda, vol. 1, Introduction, No. 3, PL IX, figs. 

 271-275. (No text reference. Figs. 271-275 are copied from Kutorga, 1848, PL VII, figs. 7c, 7a, 7b, 7b', and 7c', 

 respectively.) 



Acrotreta subconica Kutorga, von Seebach, 1865, Zeitschr. Deutsch. geol. Gesell. for 1865, Bd. 17, p. 341. (Men- 

 tioned in discussion of A. socialis.) 



Not Acrotreta subconica Meek, 1873, Sixth Ann. Kept. U. S. Geol. Survey Territories for 1872, p. 463. (This species 

 is referred in this monograph to Acrotreta idahoensis.) 



Acrotreta subconica Kutorga, Quenstedt, 1885, Handbuch der Petrefactenkunde, Aufl. 3, p. 755, PL LVIII, fig. 51. 

 (Mentioned. Fig. 51 is roughly copied from Kutorga, 1848, PL VII, fig. 7b.) 



Acrotreta subconica Kutorga, Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, pp. 600-601. (Original description 

 translated and type specimens discussed as below.) 



The original description by Kutorga follows: 



Strongly conical; the deltidium-like furrow narrow and plainly impressed. Innumerable growth wrinkles run 

 on the whole surface of the shell horizontally, and make deflections only in the furrow, the convexity of which is 

 turned toward the base of the cone. 



Height of the cone, 0.014 ; length of the base of the ventral valve, 0.012 ; breadth of the same, 0.015 . 



Four specimens, of which one is complete and three are without ventral valve. From the collection of Herr 

 von Volborth. 



On one specimen with the apex broken off I investigated the surface of the fracture under the microscope, with 

 a magnification of forty-five times, and found on it two cruriform, shallow impressions similar to those on the casts 

 of the Siphonotretes. Their surface was polished and with impressions of growth folds, and between the extremities 

 of the crura, in the neighborhood of the area-like hinge surface, a columniform fragment of the mold of the siphon. 

 From this it follows that the broken-off tip, just as the beak of the Siphonotretes, was solid and contained a cylin- 

 drical siphon. 



