87 



ACROTHYRA SIGNATA. Plate I, figs. 2 d-6. 



Bulletin Nat. Hist. Soc. of New Brunswick, vol. iv p. 377, pit- 

 xiii, figs. 2 a-e. 



Ventral valve Oval, pointed at the umbo, beak depressed and sides Acrothyra 

 compressed. Hinge area oblique. Interior. There is a strong narrow S1 

 callus, one third of the length of the valve, bounded by a raised ridge at 

 the sides and in front ; at the front of this callus is an oval pit, from 

 which a groove runs backward nearly to the apex of the shell, where it is 

 supposed to connect with the foramen. Outside the callus, on each side, 

 near the margin of the valve, are lenticular marks of the lateral muscles. 

 About the middle of the valve the position of the anterior adductors is 

 indicated by a faint impression of the lozenge or " hgart-shaped " depres- 

 sion. The margin of the valve is thickened. 



The dorsal valve is orbicular, strongly convex, and has a somewhat 

 triangular appearence, because of the sides being depressed from the 

 umbo, and because the front is strongly bent downward. Interiori 

 This shows a sharp, thin, median septum, for half of the length of the 

 valve. This ridge is broader and more distinct at the front ; at each 

 side are lateral obscure ridges diverging from the umbo. Outside of 

 these ridges are the lenticular imprints of the lateral muscles. 



Sculpture. The surface of this shell (which perhaps is not the real 

 outer surface) is shining, and has fine concentric ridges visible only 

 with a lens. 



Size. Length of the ventral valve, 3 mm. ; width, 2 rnm. ; depth, 1 

 mm. In the dorsal the length and breadth are equal, and the depth is 

 less than that of the ventral. 



Horizon and locality. This species is found in Assise b of the lowest 

 Etcheminian division at Dugald brook, a branch of Indian brook in 

 Escasonie, N.S. On a cursory examination the ventral valve of this shell 

 might pass for that of a Lingulella, but the closed deltidial area is that of 

 Acrotreta and Acrothyra ; the form of the dorsal and the nature of the 

 interior show that the species is closely related to Acrotreta. 



ACROTHYRA SIGNATA SERA. PI. I, figs. 3 a-f. 



Bulletin Nat. Hist. Soc. of the N. Brunswick, Vol. iv, p. 383, pi. xiii, figs. 3, a-f. 



Valves corneous, thick, especially the ventral. General form orbicular, Acrothyra 



signata sera, 

 with the umbo of the ventral projecting. 



Ventral valve nearly circular in outline, and with the back either 

 straight, or slightly hollowed near the apex, and rounded down toward 



