299 



Genus Macrodon, Lycett. 

 Macrodon parvus (n. sp.) 



Shell small, elongate quadrangular, or area-form ; length equal to 

 twice and a half the breadth. Valves extremely ventricose. Beaks 

 prominent and incurved, situated at about two-fifths of the entire 

 length from the anterior end. Hinge line straight, nearly as long as 

 the body of the shell. Posterior end obliquely truncate, somewhat 

 prolonged at the postero-basal angle. Anterior end gradually round- 

 ing from the hinge line on to the basal margin, which is gently arcuate, 

 with a slight emargination in the middle, forming a small byssal open- 

 ing. Hinge plate narrow, bearing on the posterior end two long 

 linear, lateral teeth ; the inner one the longest, reaching nearly one- 

 third of the length of the shell ; the anterior end having about four 

 short, oblique teeth, but less distinct than those of the posterior. Ante- 

 rior muscular scar subcircular, situated near the upper anterior angle. 

 Posterior scar larger than the anterior, with its upper margin exca- 

 vated out of the hinge plate. Pallial line entire, connecting the 

 muscular scars. 



Surface smooth, except a few concentric undulations, which are 

 scarcely visible except on the upper side of the posterior umbonal 

 slope. 



With the above characters shown on a large number of individuals, 

 it is hardly possible to refer this shell to any other than the genus 

 Macrodon. 



Genus Conocardium, Bronn. 



COXOCARDIUM PULCELLUM (n. sp.) 



Shell small, general form triangular, with ventricose valves. Hinge 

 line straight, the length equal to that of the posterior slope. Anterior 

 end cuneate ; posterior end obliquely truncate. Basal line gently 

 arcuate, widely gaping near the anterior extremity ; hiatus elongate 

 ovate, distinctly crenate on the inner border. Beaks minute, in- 

 curved, situated posteriorly ; umbonal slope rounded, posterior space 

 concave ; siphonal tube small. Entire surface marked by distinct, 

 diverging radii, those of the posterior space a trifle finer than those 

 of the body of the shell ; also by very fine concentric striae. 



This species resembles C. cannatu7n, Hall, of the Warsaw division 

 of the carboniferous limestone, but difiers in the less expansion of the 

 anterior end, in the concavity of the posterior space, and in the 

 rounded umbonal slope. C. aliforme, Sow., as figured in De Koninck's 

 Anim. Foss. pi. 4. fig. 12, except in size, is much like our shell ; but 

 specimens have not yet been obtained that measure more than four- 

 tenths of an inch in their greatest length ; while that one sometimes 

 measures one and a half inches. 



