Silurian Fossils of Nova Scotia, 153 



24. MfiaAMBONlA (?) CANCELLATA. N. Sp. Fig. 12. 



Shell sub-ovate, widening posteriorly ; beak anterior incurved, 

 umbo gibbous, with a gibbous umbonial slope on the posterior 

 side, which is scarcely diverging from the cardinal line ; posterior 

 extremity rounded, the basal margin arcuate, with a slight im- 

 pression anterior to the middle, the anterior end a little gibbous. 

 Surface cancellated by concentric and radiating elevated striae. 



It is not possible from the specimen before me to refer this 

 species satisfactorily to any known genus. 



25. Megambonia striata. N. sp. 



Shell somewhat oval, the basal and cardinal lines nearly parallel ; 

 beak sub- anterior, small ; umbones convex, scarcely gibbous ; 

 umbonial slope regularly convex, below which is a slight depres- 

 sion reaching to the postero-basal margin ; posterior end rounded, 

 fthe longer part of the curve on the basal side. Anterior end 

 short and narrow, somewhat abruptly rounded. Surface marked 

 by regularly radiating rounded striae with faint concentric lines 

 of growth. 



This diflfers from the preceding species in being less gibbous, 

 in the more nearly parallel cardinal and basal lines, in the direc- 

 tion of the umbonial ridge, and in the stronger radiating strise. 



24. AvicuLA HoNEYMANi. N. sp. Fig. 13. 



Left valve : body of the shell obliquely ovate, convex and 

 somewhat gibbous towards the umbo, anterior wing small round- 

 ed, posterior wing large triangular, obtuse at the extremity, ex- 

 tending two-thirds the length of the shell. The line between the 

 wing and body of the shell well defined by a slight abrupt de- 

 presssion along the junction. Surface marked by rounded radiat- 

 ing strise which are interrupted by fainter concentric undulations 

 or lines of growth ; the wing is marked only by concentric 

 striae. 



This species bears some resemblance to A. emacerata of the 

 Niagara and Clinton groups of New York ; but its form is slightly 

 more oblique, and the wing is marked only by concentric striae, 

 ■while in the New York species the radiating lines on this part 

 are stronger than the concentric ones. 



