368 New Species of Trilobites. 



pieces small, the facial suture half way between the dorsal fur- 

 row and the genal angle, eye rather small and situated about 

 half its own length from the posterior margin ; genal angles 

 broadly rounded. 



Thorax with ten segments, axis evenly convex, rather promi- 

 nent, full half the whole width, about one sixth longer than wide, 

 its sides nearly straight and the width at the first segment slightly 

 greater than at the last ; on each side of the axis a very narrow 

 flat space scarcely one sixth the width of the axis, its outer margin 

 forming the line of the fulcra of the pleurae ; the pleurae are in 

 length equal to about half the width of the axis, at the fulcra 

 they appear to be bent at an angle of about 45°. The segments 

 of the thorax increase in width from behind forwards. 



The pygidium is in the extent of its surface about half the size 

 of the head, transversely oval but with its lateral extremities obli- 

 quely and largely truncated, the posterior margin broadly and 

 regularly rounded, the front margin trilobed, the central lobe being 

 six eights of the whole width, the axis either not at all or only 

 very obscurely defined. 



The surface is smooth with the exception of the front part of 

 the head which is marked by fine undulating concentric fissures 

 about six in one line. The course of the facial suture has not 

 been distinctly observed behind the eye. 



Only one specimen with all the parts in place has been collected. 

 It is rolled up and its measurements are as follows. Length of 

 the head following the curvature of the surface one inch, of tho- 

 rax nine lines and of pygidium nine lines. The proportional 

 lengths of the head thorax and pygidium measured in this way 

 would therefore be t 4 o~tV~tV 



But if we measure the parts in a straight line from the middle 

 of the anterior to the middle of the posterior margins, the length 

 of the head is about nine lines, the thorax about eight and the 

 tail a little more than seven. 



The width of the head at the eyes in a straight line is one inch 

 nearly ; following the curvature one inch and a half; width ot 

 axis of thorax about seven lines ; length of pleurae about three 

 lines and a half. 



The only described species to which this bears any near re- 

 semblance is the well known I, crassicauda of Europe but on com- 

 parison I find that that species has a larger head, a narrower central 

 lobe to the thorax, the axis of the tail distinctly defined all round 



