89 



Conotreta, of Walcott, an Ordovician (Trenton) genus is a later 

 development from the Acrotretoid phylum, differing in the form of the 

 visceral callus, which is pointed in front, in place of expanding, as in 

 Acrothyra. Analogy, however, would lead us to infer that this genus 

 also was free-floating by a long pedicle, and not sub-sedentary, like many 

 species of Acrotreta. This type of Brachiopod Acrothyra is one of the 

 earliest known in the Palaeozoic rocks of Canada, being found in shaly 

 layers in the midst of the eruptives which mark the advent of Palaeozoic Antiquity of 

 Time in Eastern North America. 



ACROTYRA S1GXATA TARDA. PI. IT, figs. la-d. 



Bulletin Natural History Society of New Brunswick, vol. iv. p. 364, 

 pi. xiv, figs. 1 a-d. 



Only the ventral valve known. This is tumid, with a broad low umbo, 

 and convex on the median line. Interior. Distinguished by two short ^. .- 

 prominent grooves that end abruptly, short of the end of the callus ; the tarda. 

 callus is narrow and has a low ridge along the middle ; it ends 1| mm. from 

 the hinge, and the two lateral grooves are about 1 mm. apart. Outside of 

 the two grooves above named are low crescentic ridges in front of the lateral 

 extensions of the hinge line, that enclose the scars of the lateral muscles. 



The dorsal valve has not been separated from that of Acrotreta papillata, 

 which occurs with it. 



Sculpture. This, on the lateral slopes of the valve, consists of fine, 

 closely set ridges, visible only with a lens. 



Size. Length, 2i mm.; width, 3 mm.; depth, 1| mm. 



Horizon and locality. In the gray shales of E. 1 c and d at Dugald 

 brook, Escasonie, (C. B.) N. S. Common in the latter assise. 



This mutation is distinguished from Acrotreta papillata, with which it 

 is associated, by the form of the callus, etc., and from Acrothyra signata 

 (typical) by its flatter callus and deeper and shorter lateral grooves ; the 

 same characters distinguish it from A. signata-prima and A. signata-sera. 



ACROTHYRA SIGNATA ORTA. PI. I, figs. 4 a-j. 



Bull. Nat. Hist. Soc. of N. B., vol. iv, p. 385, pi. xiii, figs. 4, a-f. 



This rather tumid form has an overhanging beak. Ventral valve broadly Mutation 

 ovate, bluntly pointed, convex along the back, especially toward the front or 



