in the Lower Ludlow Rock. 4i7 



noso ; superficie lineis subrectis antice divergentibus tenuissime 

 striata. 



Localities. Lower Ludlow Rock, Leintwardine, with shells, 

 star-fish, and large species of Pterygotus (fig. 1, Mr. Light- 

 body's Collection; found in 1859). Upper Ludlow Rock, 

 Ludlow (in Mr. J. Harley's Collection, found in 1852). 



Of the true piscine nature of the species just described we 

 have clear evidence in the existence of all the three layers of 

 bone described by Prof. Huxley in his memoir. With regard 

 to the P. truncatuSy which is less perfectly preserved, the inner 

 layer has not yet been observed ; but in the structure and orna- 

 ment of the two outer ones — the general form, lateral angles, 

 and bevelled sutural edges — there is the closest resemblance 

 to P. ludensis. The Crustaceans of the same rocks have a dif- 

 ferent ornament, and, it is needless to say, no bony structure. 



What the relative standing of these very ancient Cephalaspid 

 fish may be, is a point yet to be decided ; but it is at least 

 worthy of note that the range of fishes a little further back- 

 ward in time is established by the discovery, not of new types, 

 but of new species of a genus and group proper to the lowest 

 beds of the overlying formation, and characteristic of these beds. 

 In the same way, the giant Pterygotiy long known in the Old 

 Red Sandstone, have now been traced downward in diminishing 

 numbers, and of new species, through all the Upper Silurian 

 beds. Again, a Pteropod and a Cystidean have been disinterred 

 from the " primordial zone " (the Lingula flags) ; but these are 

 of genera familiar to us in the true Lower Silurian rocks. An- 

 nelida, and perhaps Trilobites, recede further back than the 

 base of the Silurian ; but, as yet, the Cambrian has yielded no 

 other new and unexpected types, and, save a doubtful Zoophyte 

 or Polyzoon, no other forms at all. And if we turn to the 

 highest of the palaeozoic groups, the reptiles which have at 

 length been discovered in the Coal are found to belong to the 

 lower forms with which we have become acquainted in the 

 Permian and Trias; or, where they differ from these, it is to 

 present indications of even a still lower grade*. It is impos- 

 sible to help surmising, however unphilosophical it may appear 

 to some, that we may not be very far from the downward limit 

 of one at least of the zoological subkingdoms. If, indeed, we 

 discovered a Brachyurous crab, or a single reptile of high 

 organization in Silurian rocks, — a mammal in the Old Red, or 

 a fish in the primordial zone, such a fact would go far to demo- 

 lish the supposition. But the gradual tracing back of types a 

 little only beyond their previous limits does not appear calcu- 



* Owen, in ' Siluria,' 2nd edition, p. 363. 



