BRACHIOPODA. 101 



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

 is manifestly diiTicult 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 l)elong to this genus. Barranue's 

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

 hnng in juxtaposition to the inner opening of the foramen. 



Genus ACROTRETA, Kutorg.\. 1848. 



PLATE m, FIGS. 3-2-,il. 



1848. Acrotreta, Kutorga. Vei-hamil. der russ.-kais. mineral. Gesellsch. zu St. Petei-sburg, p. 275. 



1853. Acrotreta, Datidsox. Introduction Briti.sh Fos-sil Bi-acliiopoda, p. 133. 



1865. Acrotreta, ton Seebach. Zeitschv. der deutscli. geolog-. Ge.^ellsch., vol. xvii, ]i. 341. 



1865. Acrotreta, Billixgs. PaUeozoii; Fossils, vol. i, p. 21G. 



1871. Acrotreta (?), Davidsox. British Silurian Brachiopoda, p. 343. 



1872. Acrotreta, Meek. Sixth Ann. Kept. U. S. Geological Survey Terr., p. 403. 



1874. Ai-rotnla, White. Geograjiliical and Geological Exploration and Sui-vey West lOOtli Meridian : 



Prelim. Rept Invertebrate Fossils, p. 9. 



1875. Acrotreta, White Geogiaphical and Geological Exploration ami .Survey West 100th Meridian : 



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



1876. Aei-otreta, Llvxarssox. Brachiojioda of the Paradoxides Beds of Sweden, p. 16. 



1883. Acrotreta, Davidson. Briti.sh Silurian Biachiopoda, Supplement, p. 213. 



1884. Acrothele?, Waicott. Palaeontology 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, Tniteil Sl.ates Geological Survey, p. 98. 



Di.\GNOSis. " Dorsal [pedicle-] valve conical ; the cardinal face of the cone 

 tiat, 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- 

 \vrinkles, 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, tig. vii ; ] . 2, 3. 

 1 Systfcme Silurien Boheme, vol. v, pi. 110, tig. viii. 

 J Kdtorga, Joe. (it. 



