THE MISSISSIPPIAN PERIOD. 537 



this period and into the next, when they disappeared. The lung- 

 fishes had declined, but were represented by Ctenodus. The holopty- 

 chians had disappeared, but the crossopterygians were represented 

 by several genera that took on a closer external resemblance to modern 

 forms. 



Of the fishes frequenting the inland and coastal waters, probably 

 the culminating type was now actinopterygian of the order to which 

 the modern garpike belongs. The curious tribe of ostracoderms had 

 nearly or quite disappeared. 



The fishes probably made up the whole, or nearly the whole, of 

 the vertebrate fauna of the seas. The ostracoderms may have entered 

 the sea, as they are sometimes reported in marine faunas, but they 

 were probably fresh-water forms in the main. There are reasons for 

 thinking that amphibians frequented the fresh waters and the adja- 

 cent lands, but probably not the seas. 



II. The Land Life of the Mississippian. 



Since the period was one of sea extension and its deposits mainly 

 marine, the record of land life is poor. There was doubtless some 

 notable restriction of the terrestrial life by reason of the encroach- 

 ment of the sea. So far as may be gathered from the record, the 

 main Devonian lines were perpetuated. Enough fossil vegetation 

 has been recovered to show that all the leading groups of Devonian 

 plants were represented. There were true ferns (Archceopteris, Mega- 

 lopteris, Sphenopteris, Pseudopecopteris, etc.) probably Cycadofilices 

 (Alethopteris) , Equisetales {Catamites, Annutaria, Bornia, Astrophyl- 

 lites, etc.), Sphenopyttates (Sphenophyllum) , Lycopodiales (Lepido- 

 dendron, Sigittaria, Ulodendron, Knorria, Hatonia, etc.), gymnosperms 

 {Cordaites), and the fossil seeds Cardiocarpus, Trigonocarpus, etc., 

 commonly regarded as the fruit of cordaites. 



The most interesting suggestion of advance in land life is found 

 in the footprints of a supposed amphibian named Peteosauropus {Sauro- 

 pus) primcevus, described by Lea from the Mauch Chunk shale near 

 Pottsville, Penn. There are six double imprints, in which the track 

 of the hind foot partially covers that of the front foot. They imply a 

 stride of about thirteen inches, and a breadth between outer toes 

 of eight inches. The trail of a tail an inch wide accompanies the 

 footprints. The slab on which they are impressed is ripple-marked 



