HULLKTIX 01^ THE NATURAL HISTORY SOCIETY. 
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dividin" line at the base of the Arenig, and made the appearance of the 
Arenig graptolites the starting point of a new system. 
The beds from which this fauna was taken appear in outcrops 
along the left bank of McLeod Brook, in Boisdale, Cape Breton, X S., 
the best locality being about an eighth of a mile below the bridge that 
crosses that stream in McMullin Settlement. The rock is a soft, fine- 
grained, dark gray shale, not very different in appearance from that 
which, on the opposite side of the valley of McLeod Brook, carries the 
Dictyonema fauna. The rock easily softens when exposed to the 
weather, but is compact and firm lower down. No reference is given 
to ‘‘ locality ” in the following descriptions, as all come from McLeod 
Brook. The classes represented here are Brachiopoda, Lamellibran- 
chiata. Gasteropoda, Vermes and Crustacea. 
Acrotreta sipo. n. sp. PI. XVIII, figs. 1 and 2. 
A small species with somewhat overhanging umbo. 
Ventral valves nearly as high as long. Umbo projecting behind 
the cardinal line, somewhat bluntly pointed, (some valves are trumpet 
shaped toward the margin) and a little broader than long. Interior. 
The foramen passes outward through a short siphon which is attached 
to the dorsal side of the valve ; on each side of it are traces of lateral 
septa : in front of it is the faint impression of a callus which extends 
one-third of the distance to the anterior margin. 
The dorsal valve is transversely oval, and arched from hinge to front, 
more strongly near the hinge ; the lateral edges are flattened, especially 
toward the hinge. Interior — This shows traces of scars of lateral (?) 
muscles on each side of the umbo, and of a pair of central muscles near 
the middle of the valve. A distinct, though low, median septum 
crosses the valve nearly to the front margin. 
Sculpture . — No concentric stri;e were observed on this species, but 
the surface of the valves is minutely granulated. 
Size . — The largest ventral observed had a size at the orifice of 
3 X 3 mm., and others a height of '2}, mm. A dorsal was 2| x 3^ 
mm. ; height ^ of a mm. 
The siphon is seldom preserved. 
Three quarters of the ventral valves collected stand vertically in 
the mucl in which they were entombed. 
