504 PEOCEEDIlfGS OP THE GEOLOGICAL SOCIETY. [Jan. 19, 



bourhood of Liidlow is by far tbe largest species that has been dis- 

 covered, the cephalic plate having at least twice the dimensions of that 

 of C. Lyellii. In outline it is broadly semielhptical. In addition to 

 its large size, it is distinguished by the position, obliquity, and mag- 

 nitude of the orbits. Placed almost entirely on the posterior half of 

 the shield, these diverge from each other so as to be distant 1 inch 

 apart anteriorly, and | an inch posteriorly. The long diameter of 

 each orbit measures IJ inch. Within the orbital circumference re- 

 mains of the osseous sclerotica are visible. Owing to the backward 

 position of the orbits, it is in the posterior part of the shield that we 

 find some of the chief distinctive modifications : thus the occipital 

 crest is even shorter than that of a species less than half its size ; 

 the space between the orbital ridges is proportionately small. 



The outer enamel-layer is ornamented with tubercles, which bear 

 so close a resemblance to those covering the bony plates of Astero- 

 lepis as to have suggested the specific name. They present, however, 

 considerable variation : usually they arise by a circular and more or 

 less tumid base, which gradually terminates in an elevated papilla ; 

 or the papilla may be small, rounded, and distinct from the base. 

 Sometimes two or even three minute papillae surmount the same 

 base ; sometimes the base is quite flat and expanded, and is occupied 

 by a solitary central papilla. In all cases the base presents more 

 or less distinctly a radiated striation. The inner layer of the bony 

 plate presents lacunae and long branching canalicuh precisely re- 

 sembhng those of human bone. Many of these are completely in- 

 jected with a transparent blood-red material; and so beautifully are 

 they displayed, that one ignorant of the structure of bone would 

 be able to apprehend it by a glance at a minute part of this ancient 

 fragment. 



So wonderftQly indeed has nature treasured up her secrets in this 

 disentombed relic of a time so distant as to be incalculable, that she 

 distinctly reveals in their minutest details the structure of canals not 



more than the spoo^l^ ^^ ^^ ^^^^ i^ diameter, and such as defy the 

 skill of the anatomist to inject. 



Mr. Harley also described a more perfect specimen of CepJialaspis 

 Salweyi than the one on which Sir P. Egerton not long since deter- 

 mined the species*. It was found by Mr. Salwey at Hinstone near 

 Bromyard, and about 1| mile from Acton Beauchamp, in a sand- 

 stone similar to that in which the other specimen was found at 

 Acton Beauchamp. 



CepJialaspis Sahveyi proves to differ but very little in size and 

 external configuration from G. Lyellii. It is distinguished from this 

 species by its short and slender postero -lateral spines, which are not 

 prolonged fui'ther backwards than the termination of the occipital 

 crest. The internal parts of the posterior third of the shield form a 

 distinct, arched, nuchal plate, which is prolonged posteriorly. The 

 occipital crest is prominent, and bifurcates anteriorly into the orbital 

 ridges. These, diverging, curve a little outwards and pass to the 



* Quart. Journ. Geol. Soc. vol. iii. p. 283. 



