12 | aa 
| 
ance as the one above described. They were obtained 
from Greenville canal, in Upper Canada, and are 
imbedded in a soft, dark colored argillaceous shale, 
associated with other animal remANNgs some of which 
are exceedingiy minute. 
_ ASAPHUS TETRAGONOCEPHALUS.* Green. 
Lao Cast, No. 38. : 
Clypeo semilunari, fronte quadrato, oculis minimis, 
obscuris ; articulis abdominis duodecim 5 cauda 
rotunda, corpore depresso. 
The buckler of this Asaph, which is still found at- 
tached to the abdomen, resembles in its contour a 
long crescent ; the anterior edge in front is almost 
rectilinear ; the posterior angles or horns of the cres- 
cent, are very acute, and project a little on each side, 
- beyond the abdomen. ‘The front or middle lobe of 
the buckler, is nearly straight before, and is marked 
with two short oblique grooves on each side ; the an- 
terior groove has a little pit, or depression of the 
shell, immediately before it, on each side. The 
cheeks are remarkably large in proportion to the front, 
and there is a raised line passing over them from the 
front, nearly parallel with its edge, and also with that 
of the buckler ; this organization gives to the head a 
quadrilateral appearance, much more obvious in some 
specimens than in others. The oculiferous tubercles — 
* The Greek for “square head.” — 
