BRACHIOPODA. 
101 
Llandeilo 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 Distinct, 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. 
1848. Acrotreta, Kutorga. Verhandl. der russ.-kais. mineral. Gesellsch. zu St. Petersburg, p. 275. 
1858. Acrotreta, Davidson. Introduction British Fossil Brachiopoda, p. 133. 
1865. Acrotreta, von Seebach. Zeitschr. der deutsch. geolog. Gesellsch., vol. xvii, p. 341. 
1865. Acrotreta, 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 West 100th Meridian : 
Prelim. Rept Invertebrate Fossils, p. 9. 
1875. Acrotreta, White. Geographical and Geological Exploration and Survey West 100th Meridian : 
Final Rept., vol. iv, pt. 1, p. 53. 
1876. Acrotreta, Linnarsson. Brachiopoda of the Paradoxides Beds of Sweden, p. 16. 
1883. Acrotreta, Davidson. British Silurian Brachiopoda, Supplement, p. 213. 
1884. Acrotliele?, Walcott. Palaeontology of the Eureka District, p. 14. 
1885. Aci’otreta, 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; J 
■( Systeme Silunen Boheme, vol. v, pi. 110, fig. viii. 
I Kutorga, loa cit. 
