CHAPTER XLV 



FISHES AND SHELLS OF THE LUDLOW AND WENLOCK FORMATIONS, 



OR UPPER SILURIAN ROCKS. 



Fishes, fyc. of the Upper Ludlow Rock, PL 4.— Shells of the Upper Ludlow Rock, 

 PI. 5. — Shells of the Aymestry Limestone, PL 7. — Shells of the Lower Ludlow 

 Rock, PL 8, 9, 10 and 11. — Shells of the Wenlock Limestone and Shale, 

 PL 12 and 13. 



1. Fishes of the Upper Ludlow Rock. (PL 4.) 



Sphagodus, Agass. 

 Sphagodus pristodontus, Agass., PI. 4. f. 6 and 

 1, 2, 3. 



Pterygotus, Agass. 

 Pterygotus problematicus, Agass., f. 4 and 5. 



Plectrodus, Agass. 



Plectrodus mirahilis, Agass., f. 14 to 26. 

 (Coprolites of the Plectrodus, f. 46, 47, &c.) 



Sclerodus, Agass. 



Sclerodus pustuliferus, Agass., f. 27, 28, 29, 30, 

 31, 32, 60, 61 and 62. 



Thelodus, Agass. 

 Thelodus parvidens, Agass., f. 34 and 36. 



Onchus, Agass. 



Onchus Murchisoni, Agass., f. 9, 10 and 11. 

 — tenuistriatus, Agass., f. 57, 58 and 59. 



The researches of geologists have not yet made us acquainted with the existence of 

 fossil fishes in any strata so low in the series as the Silurian rocks, and hence the forms 

 about to be described are of great interest. They appear, in short, before naturalists, 

 as the most ancient beings of their class, which have yet been brought to light. 



In advancing our knowledge of fossil ichthyology, the discovery of these fishes has 

 also confirmed the important inference drawn by M. Agassiz, from an examination of 

 all the younger deposits ; that each great formation is characterised by species peculiar 

 to it. This doctrine is, indeed, strikingly corroborated by the evidence now produced, 

 for of the six genera above enumerated, four are entirely new, and wholly unlike any 

 forms in the overlying strata ; while the genus Onchus, though known in the Carboni- 

 ferous and Old Red Systems, is here composed of distinct species. 



In PI. 4. are figured all the remains which have been found in the highest stratum of the Ludlow 

 Rocks, constituting in parts a complete "bone hed" or matted mass of scales, teeth, jaws, and 



4h 



