BRACHIOPODA. 101 



Llaiidcilo at Coal-pit Bay, county Down, Ireland. This is a species which it 

 is manifestly difficult to separate from either A. subsidua or A. Matthewi by any 

 external or internal characters. 



The Obolus ? Bohemicus, Barrande,* from the Etage C, and Discina secedens, 

 Barrande,f from the Etage D, appear to belong to this genus. Barrande's 

 figures of the latter species show very distinctly the two tubercles or callosities 

 lying in juxtaposition to the inner opening of the foramen. 



Genus ACROTRETA, Kutorga. 1848. 



PLATE III, FIGS. 32-31. 



1S4S. Am-otreta, Kutorga. Verhandl. der russ.-kais. mineral. Gesellsch. zuSt. Petersburg, p. 275. 



1853. Acrotreta, Davidson. Introduction British Fossil Bracliiopoda, p. 133. 



1865. Acrotreta, von Seebach. Zeit=chr. der deutscli. geolog. Gesellscli., vol. xvii, p. 341. 



1865. Aci'otreta, Billings. Palaeozoic Fossils, vol. i, p. 216. 



1871. Acrotreta {?), Davidson. British Silurian Brachiopoda, p. 343. 



1872. Acrotreta, Meek. Sixth Ann. Rept. U. S. Geological Survey Terr., p. 463. 



1874. Acrotreta, White. Geographical and Geological Exploration and Survey We.st 100th Meridian : 



Prelim. Rept Invertebrate Fossils, p. 9. 



1875. Aa'otreta, White. Geogi'aphical and Geological Exploration and Survey West 100th Meridian : 



Final Rept., vol. iv, pt. 1, p. 53. 



1876. Acrotreta, Linnarsson. Brachiopoda of the Pai'adoxides Beds of Sweden, p. 16. 



1883. Acrotreta, Davidson. British Silurian Bi'achiopoda, Supipilement, p. 213. 



1884. Acrothele?, Walcott. Palasontology of the Eureka District, p. 14. 



1885. Acrotreta, Matthew. Illustrations of the Fauna of the St. John Group, No. 3, p. 36. 



1886. Acrotreta, Walcott. Bulletin No. 30, United States Geological Survey, p. 98. 



Diagnosis. " Dorsal [pedicle-] valve conical ; the cardinal face of the cone 

 flat, having a triangular form and resembling a cardinal area. From the apex 

 to the center of the base of this area runs a shallow groove, which may be 

 taken as an indication of a deltidium. At the upper extremity of this groove 

 is the suboval external opening of the sipho, which is inclined toward the 

 cardinal side. Ventral [brachial] valve flat, with a distinct marginal apex. 

 Upon the external surface of the shell are only delicate concentric growth- 

 wrinkles, which are continued over the groove on the cardinal surface ; no 

 tubercles or spines. Cardinal margin straight."! 



Type, Acrotreta subconica, Kutorga. 



* Systeme Silurien Boheme, vol. v, pi. 102, fig. vii ; 1, 2, 3. 

 i Systtme Silurien BohSme, vol. v, i;il. 110, tig. viii. 

 I Kdtorga, loc. cit. 



