179 



rounded on the ventral side ; dorso-ventral diameter (as measured on the 

 plane of the last septum preserved in the specimen) twelve lines, lateral 

 diameter nine lines ; diameter of siphuncle three lines, tapering to a point 

 at the apex ; length following the ventral curve eighteen lines. Septa 

 moderately concave and crossing the shell obliquely, so that the dorsal margin 

 is much nearer the apex than the ventral, the distances in the specimen, for 

 the septum observed being seven and eighteen inches respectively. The 

 distance of the septa from each other has not been positively ascertained, 

 none of them, except the last, being preserved. The inside of the siphuncle 

 is transversely grooved, and it is possible that these grooves may repre- 

 sent the edges of the septa. If they do, then the septa must be very thin, 

 and closely crowded together, as there are on an average about five 

 grooves in a length of one line. 



The species, so far as its characters can be made out, is a short thick 

 strongly curved form, with a large siphuncle in contact with the shell on 

 the dorsal side. 



Locality and Formation. Paquette's Rapids ; Black River limestone. 



Collector.^. Billings. 



ILL^SNUS VINDEX. (N. sp.) 



Fig. 160. 



Fig. 160. Illcenus vindex. a, Upper side of the head. 

 6, Front view of the same. 



Description. Head sub-triangular, the front narrowly rounded, thence 

 nearly straight on each side to the posterior angles, which terminate in 

 short, stout, sharp spines ; glabella depressed, semi-cylindrical, with 

 concave sides for a little more than half the length, then enlarged to 

 nearly twice the width, in front nearly vertical. The eyes are conical, 

 close to the posterior margin, sloping outwards and upwards at an angle 

 of 45, their bases distant from the dorsal furrow about three-fourths the 

 width of the glabella at its narrowest place. 



Thorax with ten segments ; axis rather strongly convex, not quite one- 

 third the whole width ; side lobes flat for half their width next the 4 axis , 

 then bent down at. an angle of about 45. 



Pygidium transversely oblong; posterior margin gently convex; sides 

 truncated for two-thirds of the whole length, and forming with the ante- 



