Point Levi Fossils, 313 



glabella rather more tban one third the width cf the neck segment, 

 thence more gradually curving inwards they reach the sides of 

 the glabella (nearly) at a point a little in advance of its length. 



Length of head in largest specimen seen four lines ; of glabella 

 about three lines ; width of glabella at base two lines, a little 

 narrower in front. Surface with the exception of the striated and 

 punctured front, apparently smooth. 



Limestone, No. I. 



Fig. 13. 



Fig. 13. — The pygidium represented by Fig. 13, appears to belong to a 

 species of Dikelocephalus, but the small fragment of stone in 

 which it occurs resembles Limestone No. 2, in which no recognis- 

 able fragments of that genus have been found. 



Genera. — x\rionellus (Barrande) and Menocephalus (Owen), 



These two genera seem to be closely related and I shall there- 

 fore notice them collectively. In Arionellus the glabella is cylin- 

 drical or sub conical with three or four lateral furrows. The 

 facial suture proceeds from the eye forward with a slight 

 inward inclination to the front margin which it cuts on a line 

 draw^n between the eye and the glabella parallel with the axis of 

 the body. Behind the eye it cuts the posterior margin at a point 

 situated on a line drawn between that organ and the outer angle 

 of the head. In the thorax of A. ceticepkalus there are from 7 

 to 16 segments according to the age of the individual. The py- 

 gidium is small. 



The head (all that is known) of Menocephalus only differs from 

 Arionellus in having the glabella exceedingly convex. Owen 

 discovered the glabella and a portion of the cheek plate but none 

 of the other parts. He describes the former as being circular, 

 highly arched hemispherical and pustulated. Judging from this 

 description and the figure given by the author and also from the 

 aspect of the associated fossils it appears to me highly probable 

 that the species which I have called Af. glohosus is not only con- 

 generic with Owen's M. minnesotensis but that it is closely allied 

 thereto, if. Sedgexoichi cannot be separated generically from 



