137 



The specimen figured has the anterior margin concealed in the matrix. 

 There are three other specimens, slightly more elongated, and with the 

 sides more concave below the carina ; more convex above. 



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

 Collector,— C. Weston. 



GONIPIIORA MEDIOCRIS. 

 Plate 9, fig. 1. 



Description. — Shell transversely elongate ; length thrice the height. 

 Ventral margin with the posterior third gently curved upwards ; a por- 

 tion consisting of a little more than the middle-third nearly straight or 

 slightly concave ; the anterior fourth rounded upwards. The dorsal 

 margin appears to be nearly straight or gently convex and sub-parallel 

 with the ventral margin for about half the length behind the umbones, 

 and then sloping downwards to the posterior angle. JBeaks nearly 

 terminal. 



The valves are strongly carinated ; the dorsal portion slightly concava 

 between the carina and the hinge-line, becoming somewhat convex on 

 approaching the posterior extremity. Below the carina the sides descend 

 with a convex slope, a very obscure concavity about the middle third. 

 None of the specimens have the anterior extremity perfect, but it seems 

 to project slightly beyond the beaks. The carina, as seen in casts of the 

 anterior, has the edge narrowly rounded or sub-acute ; it is most pro- 

 bably acute where the shell is preserved. Surface with three or four 

 striae in the width of one line, below the carina ; with finer stride above 



Length of the specimen figured twenty-four lines ; height at the 

 umbones eight lines ; depth, at about the mid-length, six lines. 



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

 Collector.— T. C. Weston. 



CyTHERODON ? PLACIDUS. (N. sp.) 

 Plate 8, fig 10. 



Description, — Cast of the interior of the right valve, oblong or 

 broadly sub-ovate ; length one-fifth greater than the height at the 

 umbones ; depressed convex j beaks a little behind the anterior third ; 

 anterior extremity broadly rounded ; ventral margin gently convex in the 

 middle three-fourths, broadly rounded up to the anterior extremity, more 

 abruptly curved up to the posterior margin ; dorsal margin occupying 



