PLATE I. 



FIG. 1. Acrothyra signata mut. prima 2| x 2 x 1 in. Mag. -f ; a Ventral valve ; b 

 Mould of interior of same ; c Ventral from the side ; d Another ventral 

 with low umbo ; e Dorsal valve ; f Mould of the interior ; g Dorsal from 

 the side. From Colbrook group at Dugald brook, Escasonie, N. S. See p. 73. 



FIG. 2. Acrothyra signata 3x2x1 mm. Mag. ] ^P ; a Ventral valve ; b Mould of 

 the interior ; c Ventral valve from the side ; d Dorsal valve ; c Mould of 

 interior of same. From Assise E. U (Lower Etcheminian), Dugald brook, 

 Escasonie. See p. 87. 



FIG. 3. A. signata mut. sera, 2^ x 2.J x 1. Mag. \ ; a Ventral valve ; b Mould 

 of interior of same ; c Ventral from the side ; d Dorsal valve ; e Mould 

 of interior ; /Dorsal from the side. From Assise E. Ic (Lower Etchemin. ) 

 at Dugald brook, Escasonie, N. S. See p. 87. 



FIG. 4. A signata, mut. orta, 2 x If x 1 mm. Mag. V* a Ventral valve, mould 

 ofinterijr showing visceral callus; 6 Another narrower, showing traces of 

 extension of the callus ; c Ventral from the side ; d Dorsal valve ; e Mould 

 of interior of the dorsal ; / Dorsal from the side. From Assise E. 2c (Lower 

 Etchemin. ) at Dugald brook, Escasonie, N. S. See p. 89. 



