52 MONOGKAPH OF DURA DEN. 



Pamphradus Andcrsoni. — Agassiz. 

 PterichtJiys hydrophihis. — Egerton. 



The bed of rock in which specimens of this genus (PI. I. fig. 1) were found, 

 is about fifty feet above the holoptychius bed, which lies in the bottom of the 

 ravine, and on a level with the rivulet which traverses it. A small project- 

 ing ledge of sandstone was cleared away twenty-four years ago, and then, 

 and never since, this singular mine of fossil wealth was laid open. The 

 fossil spot, according to the inquiries I made at the time, was literally 

 blackened by the shoal of " frog-like creatures," as the workmen termed 

 them, exposed to view ; but so friable was the stone in which they were em- 

 bedded, that few of the forms were preserved entire. Many were carried 

 away, and others speedily reduced to dust. One flag only, with thirty-three 

 impressions, and about two feet square, was saved at the time from the 

 wreck. A portion of this slab was forwarded by me to Agassiz, then resident 

 at Neufchatel ; another is now in the Agricultural Geological Museum at 

 Edinburgh ; a fragment has been deposited in the British Museum at Lon- 

 don ; and the remaining portion, in the possession of the proprietor of Dura 

 Den, has gradually yielded to the influence of decay, the figures being much 

 injured and obliterated. 



The history of this remarkable fossil is now, therefore, chiefly to be read 

 in the earlier discussions that took place immediately upon the discovery. 

 These are to be found in the Poissons Fossiles and the Monograph on the Old 

 Eed, of Agassiz ; in the Old Red Sandstone of Hugh Miller ; the Palichthyo- 

 logic Notes of Sir Philip Egerton ; and in the Course of Creation and Prize 

 Essay of the author. 



These curious crustacean fossils, when transmitted to Neufchatel, were at 

 first regarded by M. Agassiz to belong to the genus Pterichthys ; but upon a 

 more minute examination of the new group cephalaspis, coccosteus, and 

 pterichthys, Agassiz was convinced of distinctions not formerly observed. 

 " I had," he says, " at first connected pterichthys, the only species known 

 of that genus, by calling it Pterichthys hydrophilus ; but a more profound 

 study and attentive comparison of that species with the genus coccosteus, 

 have proved that it ought to form a distinct genus, intermediate betwixt 

 pterichthys and coccosteus, which I have named Pamphractus, in consequence 

 of the divided form of the carapace. The pectoral fins of pamphractus re- 

 semble very much those of pterichthys in their form — being slender, elongated, 

 and crooked. But the plates of the carapace are all differently arranged. 

 The central plate is very large {enorme) ; it covers two-thirds of the whole 

 carapace. The lateral plates, which acquire so great a development in the 

 pterichthys, are here reduced to narrow stripes, stretching to the edge of the 

 carapace ; while, on the other hand, the posterior plates are of very great 

 size, and form, with a small intercalated plate, the extremity of the carapace. 

 The disposition of the plates of the head is likewise very different from that 

 of the pterichthys, in which we discern no thoracic cincture as in that genus, 

 but a transverse line, which separates, in a striking manner, the plates of the 



