130 



Length of the best specimen collected, twenty-three hnes. Height at the 

 umbones, five and a-half lines. 



None of our specimens are perfect, and all have the outlines more or 

 less concealed in the stone. The posterior extremity seems to be narrowly 

 rounded in the lower third, nearly straight or slightly curved in the upper 

 two-thirds. It seems also to be somewhat broader than the anterior. The 

 surface characters of the posterior two-thirds of the choll, are less distinct 

 than they are in the anterior third. 



Locality and Formation, — Arisaig, Nova Scotia. Upper Silurian. 



Collector.— H. C. Weston. 



Orthonota incerta. (N. sp.) 



Plate 8, fig. 4. 



Bescription. — Shell transversely elongate, length about three times the 

 height, beaks between one-fourth and one-fifth the whole length, from the 

 anterior extremity. Dorsal margin behind the umbones straight. Ven- 

 tral margin slightly concave for about two- thirds the length, rounding up- 

 w^ards at each end. The anterior extremity is short, rounded about two- 

 thirds the whole height of the shell. The posterior extremity appears to be 

 obliquely truncated in the upper half, rounded in the lower. The valves 

 are moderately convex. From the umbones, a rounded angulation ex- 

 tends to the lower posterior angle. Above this the surface has an abrupt 

 slope upwards, becoming somewhat concave on approaching the dorsal 

 margin. A shallow concavity extends from the umbones to the ventral 

 margin. 



Surface with concentric wrinkles, four or five in the width of two lines 

 on the anterior half, becoming smaller backwards ; above the oblique 

 angulation somewhat smooth. From the umbones, backwards and down- 

 wards to the ventral margin, there are from four to six rather sharp 

 radiating, elevated lines, with concave grooves between them. 



Length of the largest specimen examined, twenty-one lines ; height at 

 the umbones, seven lines ; depth of both valves about five lines. 



The specimens are not sufficiently well preserved to exhibit all that is 

 required to determine the genus. It looks like a slender elongated 

 Goniophora. 



Locality and Formation. — Arisaig, Nova Scotia. Upper Silurian. 

 Collector.— C. Weston. 



Orthonota ? speciosa: (N. sp. 



Plate 8, fig. 3. 



Description. — Transversely elongate, ovate ; length about three times 



