FOSSIL FLORA AND FAUNA. 137 



Strange and gigantic, however, as are these early crusta- 

 ceans, they are comparatively recent discoveries and but lit- 

 tle known, and it is chiefly through its fossil fishes, their 

 numbers, variety, and beauty of preservation, that the sys- 

 tem has become the subject of popular interest and investi- 

 gation. As might be anticipated, these fishes differ consid- 

 erably in the different portions of the system those of the 

 lower being chiefly small or moderate sized, covered with 

 minute enamelled scales, and very generally armed with fin- 

 spines ; those of the middle portion, again, being fewer in 

 number but larger in size, and protected by broad sculptured 

 scales or plates ; while those of the upper zone, though still 

 covered with enamelled scales, assume more the character 

 of ordinary fishes, both in their size and configuration. 

 Throughout the whole, the bony enamelled scales and 

 plates (the exo-skeleton of anatomists) is the prevailing 

 feature, and all without exception are characterised by the 

 heterocercal or unequally-lobed tail the upper lobe extend- 

 ing in a bold and prolonged sweep, as in the existing sharks 

 and dog-fishes. In Britain the great repositories of Old 

 Red fishes have hitherto been the lower shales of Forfarshire, 

 the lower and middle flagstones of Caithness and Cromarty, 

 the middle sandstones of Moray and Banff, and the upper 

 yellow sandstones of Dura Den in Fifeshire. In some of 

 these localities they are crowded together in shoals, with every 

 fin and scale in place as if overtaken and entombed by some 

 sudden catastrophe ; and we have seen a slab about the size 

 of an ordinary writing-table, raised in Dura Den, with up- 

 wards of fifty individuals upon it, belonging to five separate 

 genera, and varying in length from ten to thirty inches.* 



* At the instance of the British Association, and under the superin- 

 tendence of the late Dr Anderson, of Newburgh, and the Author, this 

 and numerous other slabs of nearly equal richness were raised from 

 Dura Den in 1860 and 1861 ; and could they have been rendered readily 

 portable, slabs of double these dimensions, and with treble the number 



