166 



Charionella ? Hyale. (N. sp.) 



Fig. 150, a, b. 



Description. — Ovate, both valves about equally convex; length one- 

 eighth greater than the width ; apical angle about 100° ; cardinal edge on 

 each side of the beak gently concave or nearly straight ; sides gently 

 convex ; greatest width about the middle or a little above it ; front margin 

 rounded. Ventral valve moderately convex, most elevated in the upper 

 half ; umbo narrow, obtusely sub-carinate ; beak small, only shghtly 

 incurved, with apparently a perforated apex, and a deltidium below it. 

 Dorsal valve uniformly depressed convex, with indications of an obtuse 

 carination along the middle. Surface unknown. 



Length of largest specimen collected 8 lines ; width 7 lines ; depth of 

 both valves 4 lines. 



The specimens are all in the condition of casts, and as there are no 

 indications of a hinge-plate, I have referred the species to Charionella, 

 provisionally. 



Locality and Formation. — Gait. In the Guelph formation; Middle 

 Silurian. 



Collectors. — J. Richardson, R. Bell. 



Genus Trimerella. (N. gen.) 



Crenerie Characters. — Shell large, ovate or circular ; valves moderately 

 or strongly convex ; beaks solid and transversely striated, as in the genus 

 Obolus. Interior of each valve with three longitudinal septa of variable 

 length which support a horizontal flat or concave plate. In the surface of 

 this plate the muscular apparatus was either wholly or in part attached. 

 On each side there appears to be a small ovate muscular impression, as in 

 Obolus. Surface of the shell with concentric accretion ridges or striae. 

 Shell thick. 



This genus is allied to Obolus, from which it differs in the possession of 

 the longitudinal septa. 



Trimerella grandis. (N. sp.) 



Description. — Shell large, ovate, greatest width a little in advance of 

 the mid-length ; sides gently convex, front margin broadly or uniformly 

 rounded ; apical extremity apparently obtusely pointed. Both valves 

 moderately and uniformly convex ; greatest tumidity a little above the 

 middle ; umbo of dorsal valve broadly rounded. Judging from some of 



