148 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 6, 



Redonia, M. Rouault, Bull. Soc. Geol. Fr. 2 Ser. vol. viii. p. 362. 



The following generic character adds some particulars to the de- 

 scription of this curious genus, originally given by M. Rouanlt : — 



Shell equivalve, very inequilateral, with incurved beaks ; muscular 

 impressions two, the anterior one bounded by a strong plate ; hinge 

 Avith three ? strong teeth on the anterior side of the umbo on each 

 valve, and two long thui teeth on the posterior side nearly parallel 

 to the edge of the shell. 



Redonia Deshayesiana, Rouault, Bull. Soc. Geol. Fr. 2 Ser. 

 vol. viii. p. 364. Pl. IX. fig. 1. 



R. testa ovata, antice obtusa, kinula exigua depressa, postice attenuata ; 

 sulco mediano longituclinali ; liaeis concentricis inasqualibus. 



Shell ovate, anteriorly blunt, with a small lunette produced pos- 

 teriorly; with a broad, slightly marked longitudinal depression ex- 

 tending transversely from near the umbo to the margin ; concentric 

 lines of growth numerous and unequal. 



In the internal cast the umbos are produced into a point and in- 

 curved ; the anterior muscular impression is separated by a deep 

 hollow (left by the internal plate) from the umbo ; the posterior 

 muscular impression is very near the posterior margin. 



Length ^ inch, breadth 1 inch. 



Common in the Lower Silurian beds of Riba de Baixo, Valeiro do 

 Arruido, and other localities iu the Serra de Busaaco. 



It has been found by M. Rouault in the Lower Silurian slates of 

 Vitre, Gahard, and Monteuf of Brittany. 



Plate IX. fig. 1. a. Exterior, h. Internal cast. c. Hinge-teeth. 



Redonia Duvaliana, Rouault, Bull. Soc. Geol. Fr. 2 Ser. vol. viii. 

 p. 365. Pl. IX. fig. 2. 



R. testa transversim ovata, antice gibbosa ; rugis concentricis inaequalibus. 



Shell transversely ovate, anteriorly gibbose, marked with numerous 

 unequal concentric ridges : posterior muscular impression near the 

 middle of the dorsal margin. 



Length ^, breadth | of an inch. 



Found in the lower _divis ion of - the LowerSilurian formation at 

 Riba de Baixo, in the Serra de Bussaco. M. Rouault's specimens 

 are from the Lower Silurian slates of Vitre, Brittany. 



This species is readily distinguished from R. Deshayesiana by the 

 want of a Imiette and being less inequilateral ; it appears also to be 

 less abundant than that species. The position of the posterior 

 muscle also helps us to distinguish the two species. 



Plate IX. fig. 2. a. Exterior, b. Cast of interior. 



NucuLA CosT^, n. s. Pl. IX. fig. 4. 



N. testa triangulari-ovata ; lineis crebris concentricis ; dentibus cardinalibus 

 25-30 inaequalibus. 



Shell ovato-triangular, with four or five deeply impressed lines of 



