302 THE CARBONIFEROUS SYSTEM. 



Aviculopecten limestone at Windsor. The elongated form Cerato- 

 phaga is also present. 



Macrodon Hardingi, n. sp. (Fig. 102), coll. J. W. D. and Hartt, 

 from Windsor, especially in bed (e), where it is very abundant. Hinge- 

 line nearly straight, with the short cardinal teeth and long narrow 

 posterior teeth characteristic of the genus. Length about twice the 

 depth, but variable ; beak one fourth of the length from the front, 

 which is pointed, and descends with a regular curve to the straightish 



Fig. 102. — Macrodon Hardingi. 



(a)Cast. (b) Outer surface. (c) Sculpture magnified. 



or slightly incurved ventral margin. Posterior extremity truncated, 

 almost vertically, angular above, slightly rounded below. In old 

 specimens very tumid at the beaks, so that the thickness sometimes 

 exceeds the breadth. The shell, which seems to have been thick, is 

 usually represented by casts of the interior, which are smooth, some- 

 times with deep marks of the muscular impressions and a trace of a 

 rib proceeding from the front of the beak ; but when the outer surface 

 is preserved, it is seen to be covered with regular squamous concentric 

 folds, fringed at the edges with delicate radiating lines. This beautiful 

 shell, most characteristic of the upper stages of the Lower Carbon- 

 iferous limestones, is allied to Byssoarea reticulata, M'Coy, of the 

 Irish Carboniferous, and to Area M'Coy ana and anatina, De Koninck, 

 of Belgium, also to Byssoarea tumida of the Permian, — but it is 

 decidedly a new species. The specimens figured are of medium size. 

 The largest are one and a quarter inch long and seven lines thick at 

 the beaks. 



Macrodon curtus, n. sp., coll. J. W. D., Windsor, etc., with the pre- 

 ceding. — This shell differs from the last in the following particulars : — 

 It is much shorter, broad opposite the beaks, and narrowing posteriorly, 

 and covered with irregular lines of growth. As I have not seen the 

 teeth, it may belong to a different genus. On the other hand, it may 

 be a depauperated variety of the preceding, but I have no connecting 

 forms. 



Macrodon (?) Shubenacadiensis, n. sp. (Fig. 103), coll. J. W. D., 

 Shubenacadie. — Short and ovate, hinge-line straight, umbo one-third 

 of the distance from front. Posterior extremity broadly and regularly 



