672 CAMBRIAN BRACHIOPODA. 



Acrotreta Kutorga, von Seebach, 1865, Zeitschr. Deutsch. geol. Gesell. for 1865, Bd. 17, Hft. 2, p. 341. (Discussed 



in German.) 

 Acrotreta Kutorga, Davidson, 1871, British Fossil Brachiopoda, vol. 3, pt. 7, No. 4, p. 343. (Mentioned in discussion 



of Acrotreta nicholsoni.) 

 Acrotreta Kutorga, Dall, 1877, Bull. IT. S. Nat. Mus. No. 8, p. 12. (Mentioned.) 



^croircto. Kutorga, Zittel, 1880, Handbuch der Pal*ontologie, Bd. 1, Abth. 1, p. 666. (Described in German.) 

 Acrotreta Kutorga, Walcott, 1884, Mon. IT. S. Geol. Survey, vol. 8, pp. 16-17. (Discussed.) 

 Linnarssonia Walcott, 1885, Am. Jour. Sci., 3d ser., vol. 29, p. 115. (Described and discussed as a new genus.) 

 lAnnarssonia Walcott, Matthew, 1886, Trans. Roy. Soc. Canada for 1885, 1st ser., vol. 3, sec. 4, No. 4, p. 35. 



(Discussed.) 

 Acrotreta Kutorga, Oehlert, 1887, Manuel de conchyliologie, by Fischer, p. 1266. (Described in French, with 



figures of "A. subconica.") 

 Linnorssoma Walcott, Dawson, 1890, Trans. Roy. Soc. Canada for 1889, 1st ser., vol. 7, sec. 4, No. 3, pp. 53-54. 



(M'entioned in discussion of Acrothele pretiosa.) 

 Acrotreta Kutorga, Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, p. 250. 



(Described.) 

 Linnarssonia Walcott, Hall and Clarke, 1892, idem, p. 251. (Described.) 

 Acrotreta Kutorga, Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum for 1891, p. 566. (Copied 



from Hall and Clarke, 1892a, p. 250.) 

 Linnarssonia Walcott, Hall and Clarke, 1892, idem, p. 567. (Copied from Hall and Clarke, 1892a, p. 251.) 

 Acrotreta Kutorga, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 101-104. 



(Described and discussed.) 

 Linnarssonia Walcott, Hall and Clarke, 1892, idem, pp. 107-109. (Described and discussed.) 

 Linnarssonia Walcott, Matthew, 1892, Trans. Roy. Soc. Canada for 1891, 1st ser., vol. 9, sec. 4, No. 5, p. 42. (Species 



referred to the genus mentioned.) 

 Acrotreta Kutorga, Matthew, 1902, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 5, No. 20, p. 390. (Stratigraphic 



range in Cape Breton discussed.) 

 Acrotreta Kutorga, Matthew, 1903, Geol. Survey Canada, Rept. Cambrian Rocks Cape Breton, p. 94. (A copy ot 



the preceding reference.) 

 Acrotreta Kutorga, Matthew, 1903, idem, pp. 96-97. (Notes on development of the genus.) 

 Acrotreta Kutorga, Grabau and Shimek, 1907, North American Index Fossils, vol. 1, p. 199. (Described.) 

 f Linnarssonia Grabau and Shimer, 1907, idem, p. 200. (Described, but the only species referred to the genus ("L. 



pretiosa") is not figured and it is impossible to tell whether the authors are discussing the Linnarssonia pretiosa 



that has been referred to the genus Acrotreta (Acrotreta sagittalis), or to the genus Acrothele (Acrothele pretiosa).) 

 Acrotreta Kutorga, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 146. (Classifica- 

 tion of genus.) 



The original description by Kutorga follows: 



Dorsal valve highly conical; the hinge surface of the cone flat, in the form of a high triangle, similar to an area, 

 with a shallow gutter-shaped depression running from the tip as far as the middle point, which (depression) here 

 appears as an indication of a deltidium. At the upper end of this furrow, turned consequently to the hinge side, is 

 found the obtusely oval external siphonal opening. 



Ventral valve flat, with a distinct marginal apex. On the surface of the shell are seen only delicate growth wrinkles 

 concentric to the apex of the cone, which curve crescentially into the longitudinal furrow of the surface of the shell; 

 no tubercles and no spines; hinge border rectilinear. 



The revised description of the genus is as follows: Ventral valve strongly convex to conical, 

 with the posterior face more or less flattened to form a false area that is usually marked by a 

 shallow median groove. Pedicle opening at the apex of the cone and directed more or less 

 backward. Apex usually anterior to the posterior margin, but occasionally overhanging it. 

 Dorsal valve slightly convex, with very small beak; area short and divided by a small false 

 deltidium. 



Surface marked by fine concentric striae and lines of growth which cross the posterior face 

 and the median groove; in addition there are on five species veiy fine, concentric, undulating, 

 often inosculating, rounded ridges that form a surface like that of Oholus ( Westonia) ella (HaU 

 and Wliitfield) (PI. XLVII, fig. 10). Acrotreta frimseva Walcott (PI. LXIX) has this type 

 of surface. A. claytoni Walcott (PL LXXIV) has fine, undulating strise,. A. spinosa Walcott 

 (PI. LXXIX) fine short spines, and A. ? canceUata Walcott (PI. LXXIX) a cancellated surface. 

 The shell in all species where it is preserved is calcareocorneous and built up of several thin 

 layers or lamellae that are arranged more or less obliquely to the outer surface toward the outer 

 margin of the valves. 



