158 Silurian Fossils of Nova Scotia. 



tubercle at the dorsal extremity, and from four to six smaller 

 spine-like tubercles along its curve. The central ridge or tuber- 

 cle is separated from the lateral ridge by a distinct furrow, and 

 its continuation from the base of the tubercle passes between the 

 lower ends of the two lateral ridges. Ventral and lateral mar- 

 gins with a narrow thickened rim. 



This species resembles very nearly the l^. tuherculata of Klo- 

 den, as described and figured by Mr. T. Rupert Jones. In our 

 specimens the dorsal angles are more rounded ; the posterior ridge 

 at its base is never extended beyond the middle of the valve, and 

 is marked on its crest by several small spine-like tubercles. The 

 anterior ridge is usually more extended along the ventral margin 

 in our specimens, aud the furrow is better defined, while the 

 tubercles are never flattened above or overhanging the base as 

 shown in the European specimens. Smaller specimens, which ap- 

 pear to be the young of this species, present some slight variations 

 of surface markings, but show less difiference than the young of 

 B. tuherculata. 



Fig. 19. Fig. 20. 



34. Beyrichia eqilatera. N. sp. Fig. 20. 



Nearly equilateral, very convex, marked by three smooth or 

 nearly smooth ridges. The central ridge is an oblong tubercle 

 reaching from near the dorsal margin a little more than half way 

 to the ventral margin. The posterior ridge is a little larger, but 

 scarcely differing in form from the anterior one, its ventral ex- 

 tremity terminating beneath or a little in advance of the middle 

 of the central tubercle. The furrow is narrow but well defined 

 on the two sides of the central tubercle, and becoming shallow in 

 its passage to the marginal furrow ; ventral and lateral margins 

 thickened. 



35. Leperdita sinuata. N. sp. 



Minute sub-ovate, anterior end narrow, dorsal line one-third 

 shorter than the length of the valve ; an extremely minute tuber- 

 cle near the anterior end. Centre extremely convex or ventricose ; 

 ventral margin near the posterior end a little sinuous, or indented 

 from the inner-side. Surface smooth under an ordinary lens. 



