416 



FOSSILS OF THE 



[Cn. XXVI. 



previously referred some of these fragments to the class of fishes, was the 

 first to recognize their true nature, and in the first plate of his " Poissons 

 Fossiles du Vieux Gres Rouge," he figured the portions on which he 

 founded his opinion. 



The carapace of this huge crustacean, which must have rivalled, if not 

 exceeded in size the largest crabs, is furnished at its hinder part with 

 short prongs, and has two large eyes near the middle, much like those of 

 the E^irypterus found in the coal formation of Glasgow. The body con- 

 sists of ten or eleven movable rings 



(the exact number is not ascer- ^^s- ^'^^• 



tained), and was terminated by an 

 oval-pointed tail. The whole sur- 

 face is covered by the scale-like 

 markings before mentioned as or- 

 namenting the head. Prof. M'Coy, 

 to whom I owe these notes on the 

 general structure, has kindly fur- 

 nished me with a restoration of the 

 entire animal (fig. 543), which he 

 believes to be closely alHed to the 

 great Eiirypterus before mentioned, 

 if not of the very same genus, and, 

 moreover, of the same family as the 

 living King-crab or Lhnulus. 



Sir R. Murchison has expressed 

 some doubts* whether the gray 

 beds of Forfarshire, containing the 

 Pterygotus^ may not be referable to the Upper Silurian or Upper Ludlow 

 beds ; but, as they are associated at Balrudderie with numerous speci- 

 mens of Cephalasjns (the bony bucklers or head-pieces alone being pre- 

 served), apparently belonging to two species, I think it far more probable 

 that they constitute a division of the " Old Red," and perhaps not so an- 

 cient a one as the bituminous schists (6, p. 418) in the North of Scotland. 



In the same gray paving-stones and coarse roofing-slates in which the 

 Ce2:)halaspis and Pterygotus occur, in Forfarshire and Kincardineshire, the 

 remains of grass-like plants abound in such numbers as to be useful to the 

 geologist by enabling him to identify corresponding strata at distant points. 

 Whether these be fucoids, as I formerly conjectured, or freshwater plants 

 of the family Fluviales^ as some botanists suggest, cannot yet be deter- 

 mined. They are often accompanied by fossils, called " berries" by the 

 quarrymen, and which are not unlike the form which a compressed 

 blackberry or raspberry might assume (see figs. 544 and 545). Some 

 of these were first observed in the year 1828, in gray sandstone of the 

 same age as that of Forfarshire, at Parkhill near Newburgh, in the north 

 of Fife, by Dr. Fleming. I afterwards found them on the north side of 

 Strathmore, in the vertical shale beneath the conglomerate, and in the 

 * Siluria, p. 24^. 



Pterygotus problematicus, Agassiz. 

 Eestoration by Professor M'Coy. 



