102 



ACROTHELE PROLES. PI. V, figS. 3 a to 6. 



Bull. Nat. Hist. Soc. N. Brunswick, vol. iv, p. 400, pi. xvi, figs. 3 a-e. 



Acrothele General form lenticular wifch the umbo of the ventral valve projecting, 



proles. 



The length and breadth of the valves of this species are sometimes 

 equal, though usually the width is somewhat greater. 



The ventral valve is convex on all the slopes, except close to the umbo, 

 where it is slightly concave in front. The umbo is low, and is about 

 one-seventh of the length of the valve from the hinge line, the area is 

 about 1 mm. long and the length of the hinge line nearly one-third of the 

 width of the valve. Interior. This has an obscurely lozenge shaped 

 callus in front of the foramen, upon which at the posterior end is a small, 

 more elevated portion. On each side of the callus is a pair of vascular 

 ridges, marks of the advance of the central muscles. A pair of short 

 ridges, near the hinge line, are of the nature of teeth outlining sockets for 

 the articulation of the two valves. Faint curving ridges in the anterior 

 part of the valve appear to be vascular trunks ; these fork toward front, 

 and show eight or nine ridges with corresponding depressions along the 

 anterior margin. 



The dorsal valve is more regularly lenticular, but more abruptly bent 

 down behind than elsewhere, the umbo is depressed, and not easily recog- 

 nizer). Flattened valves exhibit costse radiating from the umbo, but not 

 reaching the margin. Interior. This shows a strong, broad median 

 septum extending nearly half of the length of the valve ; at the front it 

 fades away into fan-like ridges that rapidly sink to the level of the valve. 

 On each side in the cavity of the valve, and extending nearly as far for- 

 ward as the median septum and, diverging from it, is a pair of sharp 

 vascular ridges. Outside of these, on the rounded edge of the valve, at 

 the ends of the cardinal line, are a pair of elongated flattened teeth, that 

 articulate with the sockets in the ventral valve. The margins of the 

 dorsal valve are broad and rolled backward at the edges. 



Sculpture. This consists of fine, regular concentric ridges that occa- 

 sionally anastomose. There are about eight or ten ridges in the space of 

 one millimetre, the ridges being more widely spaced toward the margin. 



Size. The largest valve seen was 12 mm. long; valves of 9 mm. are 

 common ; the height of each valve is about 1 mm. 



Horizan and locality. In the shales of E. 3/1, near the top of the 

 Etcheminian at Dugald and Gillis' Brooks. Frequent. 



