OTTTER KXTBBMI- 

 TIES OF THREB 

 PiKUR^ OF 



Asaphua Hincksii, 



ON ASAPHUS HINCKSII, A NEW SPECIES. 3 



on account of the side lobes being strongly arched. The crust is 

 entirely removed from the thorax, and is only present in traces on 

 the head-shield and pygidium. The latter, like that of A. flaty- 

 ceflialus {=.Isoletus gigas), is destitute of segment-markings except 

 in faint traces on the surface below the crust, and the axis is but 

 slightly pronounced. The body-axis, with eight segments, is about 

 as broad as each of the side lobes, or perhaps a little broader — agree- 

 ing also, in this respect, with A. platycephalus. The pleurae curve 

 backwards (or towards the caudal extremity) at their points ; and on 

 each pleura— at about one- third of the distance from the point to 

 the axial furrow, and close to the upper margin — there is a small hut 

 deeply indented pit. Unfortunately, the stone is broken 

 away for a short space along the outer side of each axial 

 furrow, so that the grooving on the pleurae (if any be 

 present) is not seen. The outer halves of the pleurae 

 (speaking always as to the surface under the crust) are 

 however, quite free from any traces of a furrow. If 

 ever present, accordingly, the furrows could only have extended a 

 short distance from the axial groove. The surface of the head-shield 

 is much destroyed, but the lower end of the facial suture is seen to 

 correspond with that of A. platycephalus ; and the genal extremities 

 terminate in very slightly rounded angles. The usual asaphus-strise 

 are shewn on the margin of the shell, on both the head shield and 

 pygidium. 



Asaphus SincJcsii differs thus from A. platycephalus by the pecu- 

 liar and strongly marked indentations on the j)leur« ; and by the 

 ends of the pleurae curving backwards instead of forwards, and ter- 

 minating in well-developed points. In A. platycephalus they curve 

 forwards, and are rounded off in conformity with the rounded genal 

 angles of the head-shield. The annexed tabular distribution of the 

 four species of Asaphus occurring in Canada, brings out these points 

 of difference more distinctly. 



n 3 ^ T 13 'J.1 f Head- angles terminating in long points. — A. 

 Caudal shield with j /-. t • 

 s Lanaaensis. 

 segment furrows {^^^^ ^^^^^^ rounded.-^, mili. 



Caudal shield C Pleurae curving forwards. — A. platycephalus. 



smooth. I Pleurae curving backwards. — A. Hinchsii. 



