1858.] HUXLEY CEPHALASPIS AND PTERASPIS. 269 



succeeds it, there lies a thin dull layer, in some places of a brownish 

 colour. This is followed by an excessively delicate lamina of enamel 

 which lies upon the prisms. 



The layer of prisms is one line thick, and in section presents a 

 number of more or less hexagonal disks. The enamel passes for a 

 short distance between the prisms. Externally the prisms lie on a 

 granular layer, to which the outermost very delicate " epidermic " 

 lamina marked with parallel strise succeeds. 



M. Kner asserts (supporting his statement by the authority of 

 Heckel) that in no known fish does any such epidermic or prismatic 

 layer exist, and assuredly no such continuous internal enamel-layer, 

 as in the fossil ; and he then proceeds to compare the latter with 

 the cuttle-bone. 



M. Kner would hardly have published his views, had he sub- 

 jected his sections to a more minute and careful microscopical exami- 

 nation. But, even apart from the characteristicallv piscine structure 

 of these disks, very strong objections suggest themselves. In fact, 

 to get at any sort of resemblance, M. Kner has to compare the 

 outer layer of the fossil with the inner of the cuttle-bone, and vice 

 versa ; and even the superficial resemblance in the striation of the 

 two bodies is anything but close. 



InDunkerand Von Meyer's 'Palseontographica' (B.iv. H.3. 1855) 

 Roemer gives an account of a fossil, which he refers to the Sepiadce, 

 under the name of Palceoteuthis. Whether this body is or is not 

 a Cephalopod, is a point I will not enter upon here ; but Roemer in 

 referring to Kner's Memoir, expresses the opinion that the Pteras- 

 pides are Crustacea. 



Mr. Salter and myself described two new species of Cephalaspidce 

 allied to C. Lloydii (Ag.), in a note* appended to a paper read before 

 this Society by Mr. Banks, in December 1855. Without acceding 

 to Kner's views respecting the zoological affinities of such Cephalae- 

 pids, we adopted his name. The facts to be detailed in the present 

 paper will, I believe, fully justify this step ; and I shall hereafter speak 

 of C. Lloydii and its allies under the generic name of Pteraspis. 



Professor Pander j* has recently described two Silurian species of 

 Cephalaspis (C. verrucosus and C. Schrenckii) both from Rootsikiille. 

 The former somewhat resembles C. ornatus (Egerton), having a 

 highly ornamented and tuberculated upper surface. In the broad 

 tuberculated antero-dorsal plates, separated from the head by a suture, 

 it foreshadows Auchenaspis, Eg. C. Schrenckii has hexagonal orna- 

 mented plates upon its disk. 



Professor Pander appears to think that the margins of the disk re- 

 present jaws, being led to this conclusion, apparently, by their produc- 

 tion into short quadrate serrations, which he regards as teeth. Sections 

 of these "jaws" and "teeth," examined microscopically, exhibited 

 " a homogeneous base, in which clear and dark cells of the most 

 various forms — rounded, elongated, and angular, with fine radiating 

 branches, lay scattered, and were frequently disposed in concentric 



* Quart. Journ. Geol. Soc. vol. xii. p. 100. 



f Monographie der fossilen Fische des Silurischen Systems. 1856. 



t2 



