606 



FISHES OF THE UPPER LUDLOW ROCK. 



coprolites of fishes (see p. 199) K The fishes have been named, and are briefly described by 

 M. Agassiz, from drawings sent to him by myself, but more detailed descriptions of them will 

 hereafter appear in his great work, Recherches sur les Poissons Fossiles. 



"The figures 1, 2, Bf says M. Agassiz, "are very probably fragments of the skin (shagreen) 

 of some Placoid, of which the teeth and the vertebrae are found detached in the same beds. 

 Examine the drawing of the Squaloraia which I sent to the Geological Society 2 , and you will 

 perceive that the skin consists of similar tubercles, though these appear to me more pointed. 

 They perhaps belong to the same animal of which fig. 6. represents the tooth. This tooth is 

 sufficiently characterized to be distinguished from all those which have been already described. 

 It constitutes a new generic type, which may be designated by the name of Sphagodus, (slaughter- 

 ing or murderous tooth) and the species Sphagodus pristodontus, Agass." 



(t Fig. 4 and 5 belong undoubtedly to the same animal as the Seraphim 3 of the Old Red Sand- 

 stone. The more I know of this creature, the more I am tempted to believe that it was a fish ; 

 but how absolutely decide upon it, when we have neither discovered head nor tail, but only large 

 wings ? It may provisionally bear the name of Pterygotus problematicus, Agass. (wing fish)." 



" Figs. 14 and 26 represent the most curious fragments of fish that have yet been discovered in 

 the Silurian rocks. The teeth cannot be referred to any species already known, and constitute a 

 genus, the fishes of which were without doubt the pirates of the seas of that period. The shape of 

 these teeth, bristled with sharp points like the spurs of a cock, induce me to give it the name 

 Plectrodus (cock-spur). The marked differences which your figures display in the form of the teeth, 

 seem to indicate that this genus contains more than one species. The figures 18, 19, 22, 23, 

 represent teeth differing sensibly from those which appear among the bones, figs. 14, 15, 16, 25 

 and 26, and of which figs. 20 and 21 appear to be detached teeth. Perhaps the great number of 

 points which are visible on some of these teeth, arises from the circumstance of our seeing them 

 on their interior or exterior surfaces. If there is but one species, it might be named Plectrodus 

 mirabilis, Agass.; if there are two, that with the greatest number of points may be PL pleiopristris . 

 The coprolites (see subsequent description) figs. 46, 47, &c. are doubtless the produce of this spe- 

 cies, which fed on the small shells contained in those excrementitious bodies. The figs. 17 and 

 33 do not appear to me to differ from each other; and like figs. 1, 2 and 3, they may be the tuber- 

 cles of the skin ; perhaps they may have belonged to the skin of Plectrodus ?" 



" Figs. 27, 28, 29, 30, 31, 32, and 60, 61, 62, indicate another new type of tooth approaching 

 that of the Psammodus, but differing from it by the raised pustules on the surface : I shall name it 

 Sclerodus (rough tooth), and the species Scl. picstuliferus." 



" Figs. 34, 35, 36 represent other teeth, approaching in some respects to those of the Lepi- 

 dotus, of which I form a new genus Thelodus (mammillated tooth), and the species may be named 

 Th. parvidens" 



1 I have previously expressed my obligation to Dr. Lloyd, the Rev. T. T. Lewis, and Mr. W. Evans for their 

 exertions in developing the fossil wealth of this curious stratum or bone-bed, masses of which may be seen in 

 the museums of the Ludlow Natural History Society, and of the Geological Society of London. 



2 Now figured, Geological Transactions, vol. 5. PI. 4. 



3 The name of Seraphim was given to these singular winged bodies (Pterygotus, Agass.) by the Scotch 

 quarrymen, who first found them in the Old Red Sandstone of Forfarshire. On seeing specimens of them at 

 Edinburgh, 1834, in a collection of Mr. Lyell, M. Agassiz referred them, though with some doubt, to the class 

 of fishes. 



