ROBERTS — DISTRIBUTION OF CEPHALASPIS AND PTERASP1S. 



103 



limestones of Devon are witnesses — called by ns Old Red or Devonian ; 

 and first appeared npon the stage in true Upper Silurian times ; for 

 the Pteraspis Ludensis of the Lower Lndlow shales of Leintwardine 

 (county Salop) , is the oldest representative of the family. Its discovery 

 in these older rocks, though of great interest, did not in the least 

 surprise me ; for a sea-deposit, so clearly marked ont as littoral by 

 its starfishes and its shi^imp-like Crustacea, would be the natural 

 home of shore-fishes, which Cephalaspides undoubtedly were. 

 Moreover, the shells and fuci which the Lower Ludlow rock has 

 everywhere in keeping, tell a certain tale of its shallow- water condi- 

 tion ; and enable us by studying them to read with greater ease and 

 increased interest, the record written by succeeding seas. 



Indeed, if we are to understand the physical aspect of the Old Eed 

 age, we must make ourselves well acquainted with the foregoing 

 Silurian ; for no aid will be of greater value to us, or more beautiful 

 as a study, than the slow and gradual transition from the deep-sea 

 condition which prevailed over the border- counties I am calling 

 attention to, during the accumulation of the marine limestone of the 

 Wenlock series, and the inland lakes of brackish water, terminated, 

 probably, by wholly freshwater conditions, which have left us the 

 fine silty shales of the Upper Old Red as their legacies. 



And thus it comes to pass, that not only for the first stages of its 

 new physical career, but also for the birth-place of its life- forms, 

 the Upper Silurian age is insolublv linked with the Old Red Sand- 

 stone ; and in every exposure of these older rocks, which contain 

 littoral crabs and star-fishes, we may reasonably expect to find the 

 ancestry of the ancient shore-fishes I am describing. But though they 

 thus anticipate the age they are popularly said to belong to, they did 

 not — so far as we know — live beyond the close of the Old Red system; 

 and beyond doubt their metropolis is in the grey and red cornstones 

 of Herefordshire and Worcestershire. 



The position of these beds (see section, page 104), which are 

 seen in many places in these border counties to pass through 

 a tilestone series into the underlying Silurian, is now clearly 

 made out, and only their fossil history waits our reading. And 

 this must be learnt by us before the true contemporaneous relations 

 of the two very distinct rock-series which we together know as the 

 Devonian system can be cleared up ; before we can see what com- 

 munication, if any, existed between the shallow waters which laid 

 sandy sediment in Herefordshire, and the deeper ocean, which has left 

 us hard coral-rock and shells, in Devon. Upon the physical boun- 

 daries of these waters, Eichwald has some instructive remarks in a 

 short memoir prefacing the fish-fauna of his " Lethcea Rossica," in 

 which he points out the marked difference between fishes of the 

 shore and fishes of the open sea, and describes some new forms of 

 osseous fishes from the Devonian rocks of Russia, not unlike our 

 English Cephalaspids. And now I will mention the results of my 

 own hunting among the Old Red quarries, and I hope, by thus 

 putting others upon the trail, many good fishes may be taken. For 

 more specimens are wanted before even their (precise) position 



