i04 ON CEPHALASPIS AND PTERASPIS 



That so close an affinity obtains between all the species of Cepha- 

 laspis has, however, been disputed latter!)- by M. Rudolph Kner, who 

 in 1847 published a memoir in Haidinger's ' Xaturwissenschaftliche 

 Abhandlungen ' for the purpose of proving that C. Lloydii and C. 

 Lewisii are not piscine remains at all, but that they are the internal 

 shells of a Cephalopod allied to Sepia, for which he proposed the 

 name of Pteraspis. 



M. Kner's reasoning is based upon his examination of the structure 

 of a fossil (evidently closely allied to C. Lloydii) from the Silurian 

 rocks of Gallicia. The form of this fossil, says M. Kner, is very 

 similar to that of C. Lloydii ; but it is larger, having a length of about 

 four inches by a width of two. It consists of three layers. The 

 innermost is shining, bluish-green, enamel-like, and presents four or 

 five distinct lamellae. This laj-er forms one continuous surface marked 

 in the centre by a longitudinal depression, smaller at one end than at 

 the other, and b}' obscure radiating lines. The upper part of the 

 conical depression is covered with minute pores or depressions, which 

 are visible in the deeper as well as in the more superficial layers, but 

 become evanescent in its lower part. 



Between the layer of enamel and the prismatic layer which 

 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 the 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 liis views, had he sub- 

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

 nation. But, even apart from the characteristically piscine structure 

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

 to get at any sort of resemiblance, 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. 



In Dunker and Von Meyer's ' Palsontographica ' (B. iv. H. 3. 1855) 



