146 Silurian Fossils of Nova Scotia, 



mesial fold ; mesial fold somewhat flattened or very slightly roimd- 

 ed on the summit ; plications rounded ; surface concentrically 



lamellose. 



The specimens are all casts, or impressions of the shells. 



They bear some resemblance to S. sulcatus of the Niagara 

 group, and are intermediate between that species and the S. cyclop- 

 iera of the Lower Helderberg group. 



1, Tremastospira Acadia. N. sp. Fig. 4. 



i ■ 



Shell wider than long ; beak of the ventral valve produced and 

 incurved ; mesial depression marked by a small fold on each side^ 

 which originates about one-third of the length below the beak and 

 continues to the margin ; sinus bounded on each side by a more 

 strongly elevated plication, beyond which are six other plications 

 on each side. 



Surface marked by fine concentric stri?e. 



This shell is referred to the genus Trematospira from external 

 characters alone, which are unlike Bhynchonella proper, and the 

 shell is not a Spirifer. 



8. Rhynohospira sinuata. N. sp. 



Shell ovoid, ventricose beak of the ventral valve incurved ; a 

 mesial sinus beginning a little below the beak ; surface marked 

 by about eight or nine simple scarcely subangular plications on 

 each side the mesial sinus. 



Surface marked by concentric lines of growth. 



This species differs from the R. formosa of the Lower Helder- 

 berg rocks of New York in the plications being more slender, in 

 the more defined sinus of the ventral valve, and the continuation 

 of the two small folds in the sinus nearly to the beak. 



9. Rhynchoneila Saffordi. 



Shell varying in form from ovoid to globose. Full grown spe- 

 cimens usually wider than long, and sometimes becoming ex- 

 tremely ventricose, so that the diameter across the two valves 

 much exceeds the length. Ventral valve depressed convex, with 

 the beak minute, closely incurved ; dorsal valve very ventricosey 

 most prominent toward the front. Cardinal slope a little de- 

 pressed, sides rounded, and the front in direct line flattened but 

 not depressed. Surface finely plicated, plications little elevated^ 



