STREBLOPTERIA. 47 



Localities. — England : the Carboniferous Limestone of Settle, Yorkshire ; 

 Castleton, Derbyshire. Ireland : co. Cork. 



Observations. — I can see no sufficient reason for the recognition of the two 



species, Butotia ovalis and B. ornithocephala, de Kon., and therefore have adopted 

 the first of them. E. ovalis can be easily recognised by its large, obliquely twisted 

 umbones, and small posterior wing. 



Genus Streblopteria, M'Coy, L851. 



Streblopteria, M'Coy. 1851. Ann. Mag. Nat. Hist., ser. 2, vol. vii, p. 170. 

 1855. Brit. Pal. Foss., p. 482. 

 Meek and Worthen, 1866. Geol. Surv. Illinois, vol. ii, Palaeont., 



p. 332. 

 de Koninck, 1885. Ann. Mus. Roy. d'Hist. Nat. Belg., torn, xi, 



p. 202. 

 Miller, 1889. N. Ainer. Geol. and Palceontol., p. 514. 

 Turnquisf, 1896. Fossilfiihr. UntercarLou. Siidvogesen, Abh. geol. 

 Specialkarte Elsass-Lothringen, Band v, Heft 5, p. 60. 



Generic Characters. — Valves ovate, or rotund, the anterior side extended 

 obliquely forwards. The anterior ears small, well defined, and separated from the 

 valve by a deep slit for the byssus. The posterior wing broad, undefined, nearly 

 rectangular, extending as far as the posterior margin of the shell. Valves gently 

 convex, equivalve (de Koninck). 



Interior. — -With a short narrow tooth diverging slightly from the hinge-line on 

 the posterior side of the umbones. Ligament internal, lodged in a simple narrow 

 facet along the hinge-margin. Adductor muscle-scar large, single, shallow, placed 

 posterior to the middle line and high up in the valve. 



Exterior. — Surface smooth or with radiating ridges. 



Type species. — Streblopteria laevigata, M'Coy. 



Observations. — The genus Strebloj)teria was established by M'Coy fur Pecten- 

 like shells, with a compressed quadrate posterior wing, having a single tooth in 

 the hinge and an obliquely expanded anterior side. To this genus he referred two 

 species alone, namely, 8. laevigata and 8. pulchella, the latter only known by a 

 mere fragment, which on examination proves to be the extreme anterior end of 

 Actinopteria, probably A. persulcata, M'Coy. De Koninck doubted the generic 

 characters of this shell. Meek and Worthen, accepting the genus, propose to 

 extend it to receive shells without the peculiar backward obliquity of the typical 

 species of " Streblopteria,'" but they state that the presence of a cardinal tooth in 

 the smooth shells they propose to include in the genus is not ascertained. They 



