704 CAMBKIAN BRACHIOPODA. 



, ACEOTEETA SAGITTALIS (Salter). 



Plate LXXI, figures 2, 2a-h, 3, Sa-j. 



■Oholella sagittalis Salter, 1866, Rept. British Assoc. Adv. Sci. for 1865, p. 285. (Name proposea.; 

 Disdna labiosa Salter, 1866, idem, p. 285. (Name proposed.) 



Obolella sagittalis Salter, Davidson, 1868, Geol. Mag., vol. 5, pp. 309-310, PI. XV, figs. 17-24. (Described and dis- 

 cussed.) 

 Obolella sagittalis Salter, Davidson, 1871, British Fossil Brachiopoda, vol. 3, pt. 7, No. 4, pp. 339-340, PL L, figs. 



1-14. (Copy of preceding reference. Figs, la, 3a, 4 and 4a, 5 and 5a, 9, 10 and 10a, and 12 and 12a appeared, 



Davidson, 1868, PI. XV, as figs. 17a, 21a, 23 and 23a, 19 and 19a, 22a, 20 and 20a, and 24 and 24a, respectively.) 

 Oholella sagittalis Salter, Linnarsson, 1876, Bihang till K. svensk. Vet.-Akad. Handl., Bd. 3, No. 12, pp. 19-20, PI. 



Ill, figs. 36-41. (Described and discussed in English.) 

 Oholella sagittalis Salter, Linnarsson, 1879, Sveriges Geol. Undersokning, Afhandl. och Uppsatser, Ser. C, No. 35, 



pp. 27-28, PL III, figs. 45-49. (Described in Swedish.) 

 Oholella sagittalis Salter, Brogger, 1882, Die silurischen Etagen 2 und 3, p. 45, PL X, figs. 6-8. (Described and 



discussed in German.) 

 Oholella sagittalis Salter, Davidson, 1883, British Fossil Brachiopoda, vol. 5, pt. 2, p. 211, PL XVI, figs. 25-26. (Gives 



new localities and new figures.) 

 Linnarssonia sagittalis (Salter), Walcott, 1885, Am. Jour. Sci., 3d ser., vol. 29, p. 115, figs. 5 and 8. (Merely refers 



the species to Linnarssonia. Figs. 5 and 8 are copied from Davidson, 1868, PL XV, figs. 22a and 23a, respec- 

 tively.) 

 Oholella ida ? Dawson, 1888, Canadian Rec. Sci., vol. 3, p. 55. (Possible occurrence discussed.) 

 Obolella ida f Dawson, 1888, Peter Redpath Museum, Montreal, Canada; Notes on Specimens, April, 1888, p. 55. 

 Obolella (Linnarssonia) pretiosa Dawson, 1890, Trans. Roy. Soc. Canada for 1889, 1st ser., vol. 7, sec. 4, No. 3, pp. 



53-54, figs. 26a-c. (Discussed.) 

 Linnarssonia cf. pretiosa Dawson, Hall, 1890, idem, p. 55. (Description of the specimens discussed in preceding 



reference.) 

 Linnarssonia sagittalis (Salter), Walcott, 1891, Tenth Ann. Rept. U. S. Geol. Survey, PL LXVIII, figs. 2a-d. (Not 



described.) 

 Linnarssonia pretiosa (Dawson), Hall and Clarke, 1892, Nat. Hist., New York, Paleontology, vol. 8, pt. 1, p. 70, 



PI. Ill, figs. 43-44. (Discussed. Figs. 43-44 are copied from Dawson, 1890, figs. 26a-c, p. 53.) 

 Linnarssonia sagittalis (Salter), Hall and Clarke, 1892, idem, p. 108, figs. 60-61. (Discussed. The figures are copied 



from Davidson, 1868, PL XV, figs. 22a and 23a, respectively.) 

 Linnarssonia pretiosa (Dawson), Schuchert (in part), 1897, Bull. U. S. Geol. Survey No. 87, p. 262. (Mere reference, 



but includes specimens now referred to both Acrothele pretiosa and Acrotreta sagittalis.) 

 Linnarssonia sagittalis (Salter), Frech, 1897, additional plates inserted in 1897 in Lethsea geognostica, pt. 1, Lethsea 



palseozoica, Atlas, 1876, PL lA, fig. 3a. (No text reference. Fig. 3a is copied from Walcott, 1891a, PL LXVIII, 



fig. 2.) 

 Obolella cf. sagittalis Salter, Wiman, 1902, Bull. Geol. Inst. Univ. Upsala, vol. 6, pt. 1, No. 11, p. 66. (New localities 



mentioned.) 

 Obolella (Acrotreta ?) sagittalis (Salter), Moberg and Segerberg, 1906, Medd. fran Lunds Geol. Faltklubb, Ser. B, 



No. 2 (Aftryck ur K. Fysiografiska Sallskapets Handl., N. F., Bd. 17), p. 64, PL I, figs. 25 and 26. (Charac- 

 terized in Swedish.) 

 fLinnarssonia pretiosa Grabau and Shimer, 1907, North American Index Fossils, vol. 1, p. 200. (Described, but 



not figured, and it is impossible to tell whether the authors are discussing the L. pretiosa that is now referred 



to Acrotreta sagittalis, or the true Acrothele pretiosa.) 



Although I have examined a large collection of tliis species, both from Wales and Sweden, 

 good exteriors of the valves have not been observed. The apex of the ventral valve almost 

 invariably remains in the matrix, or the shell has been removed by solution. The convexity 

 of the two valves is approximately the same (figs. 3c and 3d, PI. LXXI) except that the ventral 

 valve is more elevated near the apex. The apex is situated a little in front of the posterior 

 margin at the edge of the slightly defined false area which slopes forward at an angle of 70° 

 to 80°. The surface of the shell is marked by rather strong concentric striae and often 

 strong ridges of growth and very fine radiating striae on the interior layers. The shell is built 

 up of thin layers or lamellEe of a calcareocorneous nature. The average diameter of specimens 

 from St. Davids, Wales, is 2.5 mm. The representatives of the species from Andrarum, Sweden, 

 are usually smaller than the St. Davids shells but otherwise appear to be identical. 



The interior of the ventral valve is shown by numerous casts. The apical callosity and 

 the cardinal scars are usually large. The visceral cavity is sometimes outlined in front of the 

 callosity and between the clearly marked main vascular sinuses. Casts of the interior of the 



