i2 



Thus, in some much compressed specimens which on that account would 

 be referred to M. compressus, the umbones are terminal and overhang 

 the anterior end, and there is a somewhat deeply excavated lunule, as 

 in the typical M. Canadensis. The anterior half of a left valve of a 

 Megalomus from Durham represented in the wood-cut, fig. 2, on the 

 preceding page, be longs to a specimen which is almost exactly inter- 

 mediate in its characters between M. compressus and M. Canadensis. 



Connecting links between the two forms are so frequently found as 

 to suggest the conclusion that M. compressus is only a variety of M- 

 Canadensis, a view which is identical with that expi-essed in 1852 by 

 Prof. Hall, who after examining a large number of examples of Megal- 

 omus, states that he is " unable to find any characters indicating more 

 than a single species." 



According to Dr. E. Bell, the first discoverer of this curious genus 

 waa his father, the Eev. Andrew Bell, then of Dundas, who sent speci- 

 mens of the typical species to Prof. Hall in 1847 or 1848. 



Anodontopsis concinna. (N. Sp.) 

 Plate 2, fig. 4, and plate 7, figs. 4 & 4a. 



Small compressed — convex, about one-third longer than high, very 

 inequilateral, outline subtrapezoidal : anterior end short, rounded and 

 rather narrow, posterior end larger and wider, its upper and lower 

 margins being nearly parallel, and its extremity somewhat obliquely 

 truncated : dorsal mar'gin straight and almost parallel behind, sloping 

 rapidly and obliquely downwards in front : ventral margin nearly 

 straight but slightly convex in tlie middle, rounding upwards very 

 abruptly at the anterior end, and ascending to a much less height and 

 in a very gentle cm-ve to its subangular junction with the basal margin 

 of the posterior extremity. Umbones broad and angulated behind, 

 beaks small, not prominent, directed forwards and situated about half 

 way between the centre of the shell and the outer boundary of the 

 anterior end. Posterior area not distinctly defined, consisting of a very 

 oblique, concave inflection of the valves bounded by a faint angulation 

 which extends from the beaks towards the posterior end of the base 

 but which becomes nearly obsolete in the lower half of the shell. 



Surface markings and hinge dentition unknown. 



Length of the largest specimen collected, twenty-five millimetres : 

 maximum height of the same, seventeen mm. 



Gait, T. C. Weston, 1867 : a cast of a right valve. Dm-ham, Mi-. J. 

 Townsend : a perfect cast of both valves, which, however are both 



