134 



only about one-tenth the whole length of the shell, beyond the beaks. 

 From the beaks a moderate angulation extends obliquely backwards and 

 downwards, to the posterior ventral angle. Above this the slope to the 

 dorsal and posterior margins is flat or obliquely concave. 



Surface, at the anterior extremity, with strong rounded concentric 

 ridges, four to six in the width of two lines, their number increasing on 

 the sides of the shell, both by sub-division and intercalation, while they 

 become flatter and broader. On crossing the carina, the strise form a 

 narrowly rounded curve, and turn upwards to the hinge-line, running par- 

 allel to the obliquely truncated posterior margin. Where the surface is 

 perfect, a set of very fine stride may be seen on and between the principal 

 ridges. On one of the specimens there is an obscure elevated Hne run- 

 ning from the umbones downwards to the ventral margin, which it reaches 

 a little behind the mid-length. 



Length of an averaged sized specimen, sixteen hnes ; height of the 

 same at the umbones, about seven lines ; height at the posterior extremity 

 of the hinge-line, about eight lines. 



Localitij and Formation > — Arisaig, Nova Scotia. Upper Silurian. 

 Collector,— C. Weston. 



GONIOPHORA TRANSIENS. (N. Sp.) 

 Plate 8, fig. 7. 



l)escri])tion. — Shell transverse, sub-rhomboidal, moderately and irre- 

 gularly convex, with an acute, gently sigmoid angulation, extending from 

 the beaks backwards to the lower posterior extremity ; beaks situated at about 

 the anterior third of the length, closely incurved ; ventral margin gently 

 convex, slightly sinuated in the middle ; dorsal margin somewhat straight, 

 anterior extremity uniformly rounded, occupying somewhat over two-thirds 

 the whole height ; posterior margin obliquely truncated, slightly convex, 

 forming with the dorsal margin an angle of about 135 ^ ; the lower pos- 

 terior angle is acute, nearly on a line with the ventral margin. 



Behind the carina, the surface descends with a flat or gently concave 

 slope, to the posterior and dorsal margins. At the beak, a flattening of 

 the surface (or a slight concavity) commences, and, gradually widening, 

 extends to the ventral margin, occupying rather more than the middle 

 third of the side of the shell. The concavity occurs a little in front of 

 the mid-length. The flattening extends backwards to the carina. The 

 anterior third is moderately convex. 



Surface in the anterior third with rather strong, rounded, concentric 



