34 The Ottawa Naturalist. [May 



narrow and consisting of a small rounded lobe below the beaks, 

 on each side ; posterior side longer, and a little wider in the direc- 

 tion of its height ; posterior end vertically subtruncate at its mid- 

 height, rounding abruptly into the cardinal margin above and into 

 the ventral margin beloiV. Ventral margin gently convex but curv- 

 ng upward more abruptly and rapidly at the posterior than at 

 the anterior end ; superior border almost straight and nearly 

 horizontal ; umbones depressed, anterior, very nearly but not quite 

 terminal ; beaks incurved. 



Surface markings not at all well preserved in either of the 

 specimens collected, but apparently consisting of fine concentric 

 lines of growth. Hinge dentition and muscular impressions un- 

 known. 



Approximate dimensions of the specimen figured : maximum 

 length, fifteen millimetres; greatest height, eleven mm.; maximum 

 width, or thickness through the closed valves, nearly nine mm. 



Trenton limestone, Ottawa, E. Billings : four nearly perfect 

 but badly preserved specimens. 



M. brevis can be distinguished at a glance from M. tener, M. 

 rugosa and M. recta, by its comparatively short, tumid and regu- 

 larly convex valves. 



Ottawa, April i6th, 1903. 



REPORT OF THE ZOOLOGICAL BRANCH, 1902. 



To the President and Council of the 



Ottawa Field-Naturalists' Club. 

 In submitting the usual report referring to the zoological 

 work of the Club during the past year, it must be admitted that 

 no very new or striking facts are available such as would give 

 special interest or value to this annual record. Many years ago 

 the leaders of the Zoological section pointed out that original 

 observations on our native mammals are becoming more diflficult, 

 as the city continues to expand and the surrounding country be- 

 comes more thickly occupied, and they specified the moles, the 

 shrews, and the smaller rodents as likely to afford the main field 



