in the Lower Ludlow Rock. 45 



to make it known, the more so as all previously-described fishes 

 from the Silurian system, other than those of the very topmost 

 layer (the bone-bed), have, when carefully examined, turned 

 out to be something else than fish. Zoophytes, Trilobitc-frag- 

 ments, plates of Cystidean animals, the tail-spines of Crustacea, 

 even worm-burrows and scales of black mica, have all been mis- 

 taken for fragments of fish-bones or scales, and have some of 

 them figured even in general works. The only undoubted spe- 

 cimen (a fish-palate) was described from rocks of the age of the 

 Dudley limestone ; but this has proved to be a Carboniferous 

 species*, and was most probably introduced by accident into 

 the quarry of older rock, among the debris of which it was 

 picked up. 



It is therefore a matter of real interest to find at length a 

 true Vertebrate down in the mud-stones of the Lower Ludlow 

 rock, many hundred feet below the bone-bed. The position of 

 the fossil is unquestionable ; its place has been determined by 

 one of the most persevering of our local geologists, Mr. Light- 

 body of Ludlow, who (in company with Mr. Lee of Caerleon) 

 found it, and in whose collection the gem remains ; and it has 

 been verified by others, the Rev. W. Symonds of Pendock espe- 

 cially, who, as well as myself, has seen the quarry, and knows 

 well that these flat-bedded strata belong to the Lower Ludlow, 

 are full of the characteristic fossils, and are regularly surmounted 

 by the Aymestry limestone and the Upper Ludlow rock. 



The place of the fossil thus secure, its structure is the next 

 point of importance ; and those who have read the memoir on 

 Pteraspis in a late volume of the ' Quarterly Geological Journal f 

 will be satisfied with the statement that both the prismatic inner 

 or second layer, and a good deal of the outer striated layer, are 

 preserved on this nearly complete dermal plate — the portion 

 usually preserved, and which was shown, at the last Meeting of 

 the British Association J, to lie immediately behind the head, on 

 the dorsal surface. 



Description. — This nuchal plate shows a very similar form 

 and striation to that of Pteraspis truncatus § from the topmost 

 layers of the Ludlow rock (or Downton sandstone), but it is 

 longer and narrower, and of much less depth and convexity. 

 This is not due to pressure; for an Upper Ludlow specimen, 

 undistorted, has the same characters. The general form is a 

 long oval, with the ends truncated ; the front is slightly emar- 



* Cochliodus aliformis, M'Coy. See Quarterly Geol. Journal, vol. vii. 

 p. 266. figs, a, b, c. 



t Prof. Huxley, in vol. xiv. p. 26", &c. 



X Id. in Rep. Brit. Assoc, for 1858, Trans. Sect. p. 82. 



§ See Banks in Quart. Geol. Journ. vol. xii. pi. 2. f. 1. 



