284 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 25, 



of the orbits. The diameter of each eye-socket in Cephalaspis Lyellii, 

 as compared to the interspace between them, is as one to one, whereas 

 in the new species it is as three to five, and this without any disloca- 

 tion or fracture, on comparison of the specimens compared, by which 

 to account for so great a discrepancy. Some doubt has hitherto 

 been entertained as to the true homology' of the orifices which I have 

 considered as the orbital depressions, in consequence of the absence 

 of these features in Cephalasjns (Pteraspis) Lewisii and Lloydii. 

 Mr. Salwey's specimen resolves this doubt satisfactorily, for it ex- 

 hibits unmistakeably the cast of the sclerotic coat of the eye-ball 

 (PI. X. fig. 1 b). 



There remains another character to be mentioned corroborative 

 of the specific distinction of Mr. Salwey's Cephalaspis. It is need- 

 less to occupy time with a description of the structure of the several 

 bony laminse of which the buckler is composed, which corresponds 

 with that already published of the analogous parts in C. Lyellii. 

 There is, however, a striking difference in the surface-ornament of 

 the outer or dermal layer. This does not present a continuous stra- 

 tum of enamel investing the subjacent bone, nor does it exhibit any 

 of the parallel striations seen in other species of the genus ; but the 

 enamel occurs in small drops or splashes, scattered here and there 

 irregularly over the surface, resembling somewhat the ornament in 

 the head-bones of Coccosteus ; the granules, however, being fewer in 

 number and less regular in shape and disposition (PI. X. fig. 1 c). 



It is much to be desired that other specimens of this species may 

 be brought to light, since much remains to be known as to the form 

 of the shield, which I am inclmed to think differed considerably 

 from the regular crescentic outlines of Cephalaspis Lyellii. I have 

 named this species Cephalaspis Salweyi, after its discoverer. 



Cephalaspis Murchisoni, spec. nov. PI. IX. fig. 1. 



Two specimens collected by Mr. Lightbody in a bed below the 

 Paper-mill on the Teme at Ludlow afford presumptive evidence 

 of a new species of Cephalaspid, about the size of Cephalaspis 

 Lyellii. One shows the concave inner surface of the cranial cavity, 

 the other is a cast of the buckler of a smaller individual with some 

 portions of the bone still adhering. The larger one, being the more 

 perfect, is selected for description ; but so far as the state of pre- 

 servation of the specimens will admit of comparison, there is a perfect 

 agreement between the two. The occipital crest is wanting ; but, as 

 the posterior margin of the buckler is preserved up to a point in 

 close proximity to the crest, the comparative measurements will be 

 taken from that point. From thence to the extremity of the snout 

 the dimensions are 2 inches j\7ths. From a central point on the 

 median line, between the orbits, to the snout, is 1 inch f^ths ; and 

 from the same point to the hinder border of the shield, 1 inch jxr^h. 

 The diameter across the line of the orbits is 2 inches j^ths. The in- 

 terspace between the orbits is rather less than the diameter of the orbit. 

 As several of these dimensions must necessarily vary, subject to 



