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Contributions to Palaeontology. 



distinctive In their form and in their posterior extension. 

 The surface-marking in both species, but particularly in 

 D. granulosus, is very peculiar, and unlike anything known 

 in typical species of Dikelocephalus. I have found it 

 necessary, therefore, to separate them from the latter genus. 

 At the same time there is equal difficulty in referring them 

 to any established genus, so far as I have access to pu- 

 blished scientific works. I therefore suggest a distinct 

 generic term that may include these two species, which, 

 from present knowledge, I regard as similar generic 

 forms, 



GENUS PTYCHASPIS (n. g.). 



[ Gr. fliTu^?], plicatura) OLtftfig, scutum.'] 



Head broad and strong, with wide depressed-convex 

 cheeks. Glabella cylindrical, convex, deeply lobed or 

 transversely furrowed, very prominent in front. Eyes 

 anterior to the middle. The facial suture cutting the 

 anterior border at a point between the eye and the gla- 

 bella, or almost in front of the eye ; and from below the 

 eye it proceeds obliquely and in a slightly curving line 

 to the base, at a point near to, or a little without the 

 centre of the cheek, leaving the movable cheek of nearly 

 the same dimensions as the fixed cheek. Movable cheeks 

 sub trapezoidal, with a strong thickened border, which is 

 extended into a spine. Eyes unknown. Palpebral lobe 

 in one species, small. 



The general direction of the facial suture is similar to that 

 of Arionellus ; but the eye is more anterior, though 

 of the same form. The strongly lobed cylindrical or 

 subcylindrical glabella is a very distinctive feature. 

 Thorax with strong articulations, the axis elevated, and 

 the annulations marked by a broad node at their ex- 

 tremities : ribs marked by a subcentral groove, and 



