62 THE TRIAS AND OOLITE. 



preceding systems. The pentacrinite, instead of a round, has 

 a five-angled stalk, with an increased profusion of tentacula ; 

 it had also the superior character of a power to float about, 

 and attach itself where it pleased. To this fossil of the lias 

 succeed others of the same family in the oolite comatula arid 

 ophiura which are entirely free-swimming, thus supporting 

 the general appearances of an advance of animal characters as 

 we proceed from lower to higher formations. Here also 

 appear other examples of the order to which the crinoidea 

 belong (echinodermata) ; namely, the echinus, or sea-urchin, 

 and the goniaster, which last is regarded as a link between 

 the echinus and star-fish. 



Among the crustaceans of the oolite, a conspicuous place is 

 due to the limulus, or king-crab, of which several species 

 occur in this formation. This animal is remarkable as the 

 genus of our time to which the trilobite makes the nearest 

 approach ; and the appearance of the limulus at the time 

 when the trilobite vanishes, (the carbonigenous era,) is 

 spoken of by a distinguished geologist as " one of those 

 beautiful links in natural history, of which the strata forming 

 the earth's crust have afforded so many proofs." ( 37 ) Here 

 also we have, in the eryon, an early example of the highest 

 crustacean order, (decapoda,) and one to which the modern 

 lobster and cray-fish belong. Insects resembling the dragon- 

 fly have been found in the oolite. 



The deeper oolitic seas were occupied by various species of 

 terebratula, a brachiopodous mollusk remarkable as having 

 lived in one form or another from the earliest to the present 

 time. In the shallower seas were other bivalves. There was 

 also abundance of all the univalve classes, Pteropoda, Gastero- 

 poda, and Cephalopoda. Of the last we see an advance of 

 characters in the ammonites and belemnites, which now 

 appear in many varieties. The belemnite, which belonged 

 to the higher order of the class, those having only two 

 branchiae, calls fur some particular notice. It is an elongated, 

 conical shell, terminating in a point, and having, at the larger 

 end, a cavity for the residence of the animal, with a series of 

 air-chambers below. The animal, placed in the upper cavity, 



