MESOZOIC TIME — CRETACEOUS. 869 



The Palms came in during the Middle Cretaceous as the decline of the 

 Cycads made progress. It is supposed probable that they were in the 

 successional line of some type of Cycads, since they approach them in their 

 foliage, in their usually simple stems, and in having the pithy interior 

 traversed by bundles of woody fibers. 



Progress in MoUusks : Culminations under the type. — The Tetrabranch 

 Mollusks, which include- the Nautilus and Ammonite tribes, pass their climax 

 and decline in the Cretaceous period. The Nautiloid, which commenced 

 with a straight body and a shell no longer than the little finger, and was 

 continued in carved and coiled forms, and reached its maximum in the 

 Carboniferous, is continued to the present time, but only in two or three 

 species of Nautilus ; and these are the last of the Tetrabranchiates. The 

 Ammonite section, which commenced with the closely coiled Goniatite in 

 the Early Devonian, became increasingly complex in the flexures of the 

 septa, and finally two to three feet in diameter in the Jurassic and Cretaceous 

 seas, where it numbered thousands of species. It disappeared entirely, or 

 nearly so, at the close of the Cretaceous. 



The Dibranchiate Mollusks, or the Cuttle-fishes, whose shells are internal 

 when any exist, are known first from the later Triassic beds. Under the 

 Belemnite family they become very numerous in the Cretaceous, and 

 apparently end at its close. But other Cuttle-fishes were continued; and 

 probably the giant species of modern Newfoundland and other seas, having 

 bodies 12 to 15 feet long, arms of 25 feet, and eyes of 8 inches diameter, the 

 largest in the animal kingdom, are evidence that the type, and the type of 

 Mollusks, has now its time of culmination as to grade of species, though 

 not as to numbers and predominance in the marine fauna of the world. 



Fishes : their cxdmination in Mesozoic time. — The type of Fishes is 

 supposed to have culminated as early as the Triassic in the Ceratodus and 

 related Dipnoans, which have rudimentary arms in the fins, essentially 

 lungs as well as gills, and other Amphibian-like characteristics. The line to 

 the Teleosts, through the Amioids, was a declining line. In some respects 

 the Teleosts are more highly specialized, but not in a way toward superiority ; 

 they are purer representatives of the Fish-type, and better illustrate the fact 

 that the Fish-type is a low style of Vertebrate. The Selachians hold to 

 their early characteristics of a cartilaginous or semiosseous skeleton, of gills 

 without gill-covers, and of a heterocercal or vertebrated tail. The Cestraciont 

 Sharks, which were common in the Cretaceous, became fewer afterward, and 

 now only four species exist — and these live in Australian and Japan seas. 

 The Squalodonts, or Sharks of modern type, reached later their time of 

 maximum display. 



Decline in Amphibians. — Amphibians, so far as registry gives evidence, 

 were few in species after the Triassic period. In the scale-covered and large- 

 toothed Labyrinthodonts of the Permian or Triassic periods they passed their 

 maximum as to size, grade, and numbers. No American, British, or Euro- 



