NATURAL HISTORY OF THE I'lUMEVAL WORLD. 



29 



III the Crustacea the principal existing genera would 

 seem to have been the Cythcris, Cytiiere, and Banilia; 

 among the Malacostraceans, those huge lobsters and 

 sea-crabs known as the Patjurus, Notojmcorystcs, and 

 Mi/cria. 



A deservedly-popular writer shall complete for us 

 the picture of Cretaceous life : — 



It was now, he says, that the minute Polyzoa, or 

 Sea-mats, wove their delicate tracery of network in a 

 thousand forms {Flustra, Eschara, Diastopora, Actlno- 

 pora, Idmonca), spreading it over corals, dead shells, 

 and crustaceans, as if their function had been to shroud 

 in beauty the worthless and decaying wreck of the 

 Cretaceous sea-shore. 



The higher Mollusca also appear in vast profusion — 

 many of the Oolitic genera having departed or being 

 on the decline, while other forms peculiar to the chalk 

 begin to make their appearance. The deep-sea ISra- 

 chiopods are represented by species of Tcrehratiila, 

 Terebratella, and Rhynconella ; the true Bivalves by 

 Inoccramus, Lima, Ostrea, Pectsn, Astarte, Cardiuin, 

 Tnrjonia, Venus, and many others, whose specific 

 forms are new and peculiar to the period; while Gas- 

 teropods, like Natica, Littorina, Cerithmm, Rostellaria, 

 Solarium, Pleurotomaria, and others, mark a busy 

 sea-shore of herbivorous and carnivorous activity. 



The Cephalopods, though numerically fewer than in 

 the Lias and Oolite, now appear in cmiously fiintastic 

 forms. The chambers of the shell-clad genera had 

 previously been straight as an arrow, like the Orthoccrus, 

 or coiled on the same plane, like the Nuulilus and 

 Ammonite, But now some of them appear bent like 

 a hook [Hamitcs), curved like a boat's prow {Scapititcs), 

 incurved like a crosier [Ancyloccrus], twisted like a 

 ram's horn {Crioceras), spun round a straight axis, 

 and tapering like a spire or a pagoda {Tiirrilites), or in 

 some other fanciful and simulative guise. Examining 

 these elegant memorials of the past, we are reminded 

 of the poet's exclamation : — 



" See wlmt a lovely sliell. 

 Small and pure us pearl. 

 Lying close to my foot ; 

 Frail, but a work divine 

 Made so fairiiv well, 

 With delicate spire and whorl, 

 How exquisitely minute, 

 A miracle of design ! 



The tiny cell is forlorn, 

 Void of the little living will 

 That made it stir on the shore. 

 Did he stand at the diamond door 

 Of his house in a rainbow frill V 

 Did he push, when he was uncurl'd, 

 A golden foot or a fairy horn 

 Through his dim water-world?'* 



This abundance, this wonderful profusion of generic 

 types, and that on the very eve of their decline, has 

 originated numerous hypotheses. Those writers who 

 consider the modification of form to depend upon 

 physical conditions, suppose that certain obnoxious 

 changes in the waters of deposit were the proximate 

 causes of these fantastic and singular forms. " It is 

 true," says Dr. Page, "that an influx of fresh water 

 into a marine area, or vice versa, is often attended by 



curious changes in the indwelling Mollusca, and that 

 new conditions of cultivation produce strange sports 

 among the varieties of the gardener ; but the forms of 

 these Cretaceous shells are too decisive and persistent 

 to be otherwise explained than by supposing the intro- 

 duction of new genera, in obedience to some great but 

 unknown law of creation." 



The fishes of the chalk formation include many of 

 the old Placoids and Ganoids (the Sharks, Rays, and 

 Sauroids) of the Oolitic, but with new and peculiar 

 genera of the same great divisions ; while for the first 

 time the Ctonoids and Cycloids, which in our present 

 seas are the prevailing orders of ichthyic life, make 

 their appearance. 



Among the Placoids the dominant genera were — • 

 Ptychodus, Hyhodus, Acrodns, and Lamna; among 

 the Ganoids — Gyrodus, Pymodus, and Macropoma ; 

 among the Cycloids— Osmcroides, Hypsodus, Suiiro- 

 ccplmlus; among the Ctenoiils — Bcri/x and Berycopsis. 



We now turn to the Keptiles, and find a few species 

 of the Plosiosaurus and Ichthyosaurus still dragging their 

 huge bulk through the ocean waters. On the land an 

 Iguanodon or two still crawls among the herbage, and 

 from the sea-cliffs the ungainly Pterodactyles still 

 essay their awkward, dropping flight. The Crocodiles, 

 Lizards, and Tmtles are represented by several genera ; 

 but it is evident that, on the whole, the meridian of 

 reptile life is past, and that if the colossal types of the 

 Oolitic are not wholly extinct, they are rapidly dis- 

 appearing. Few and faint are the traces as yet dis- 

 covered in the chalk of birds and mammal.-;, and in this 

 direction there remains much valuable and important 

 work to be accomplished by the future geologist and 

 paleontologist. 



Our description of the series of Secondary strata 

 may fitly conclude with Dr. Buckland's summary : — 



The peculiar feature in the population of these 

 series was, as he points out, the prevalence of numerous 

 and gigantic forms of Saurian reptiles. Many of these 

 were exclusively marine ; others amphibious ; others 

 were terrestrial, ranging in savannahs and jungles, 

 clothed with a tropical vegetation, or basking on the 

 margins of estuaries, lakes, and rivers. Even the air 

 was tenanted by flying lizards, under the dragon form 

 of Pterodactyles. The earth was probably at that 

 time too much covered with water, and those portions 

 of land which had emerged above the surface were too 

 frequently agitated by earthquakes, inundations, and 

 atmospheric irregularities, to be extensively occupied by 

 any higher order of quadrupeds than reptiles. 



It is worthy of notice that, in the Cretaceous period, 

 the forms of vegetable life begin to approximate very 

 closely to those which now obtain. The types may 

 now be recognized of the maple, the alder, the walnut, 

 the wych-elm, and other dicotyledons; and the palms 

 include several species which difler but little from those 

 now flourishing under tropical skies. 



" As we retirefrom the days of the primitive creation," 

 says Lecoq, " and gradually approach those of our own 

 era, the sediments seem to withdraw themselves from 

 the polar regions, and we find them restricted to the 

 temperate or equatorial zones. The great beds of sand 

 and limestone constituting the Cretaceous formation, 



