74 EVOLUTION IN THE PAST 



NAUTILOIDS Some old-fashioned, straight-shelled forms were still in. 

 existence (Orthoceras) ; but their protracted annals were 

 now about to close. Coiled nautiloids held an easy domin- 

 ance ; and some old species that had been slowly developing" 

 into the condition of the living Nautilus had now almost 

 reached the goal. 

 AMMONOIDS The greatest activity in development was among the 

 Ammonoid cephalopods. The Goniatites had wellnigh dis- 

 appeared, or been transformed ; and practically aU Triassic 

 members of the Order may be described as Ammonites. The 

 creatures, as a rule, had their shells in a far more portable 

 condition, as shown by the compUcated sub-surface patterns. 

 These twisted markings had assumed ornate characters, and. 

 resembled in many cases smaU fohage delicately indented. 

 (Phyllocampyli). In addition to this concealed beauty, many 

 shells, owing to modifications on the edge of the mantle or 

 body-skin, were highly decorated on the exterior (Pachy- 

 campyli). 



Conditions were extremely favourable to ammonites for- 

 the greater part of the Period. They abounded in an im-- 

 mense variety of forms, their sheUs differing not only in 

 sub-surface tracery, and outward ornamentation, but also in 

 shape and strength. 



Their range was world-wide, and they certainly attained . 

 their climax in this Period, but before its close some signs 

 of breakdown became evident. 

 BELEMNITES Just as these signs were appearing, Cephalopod-hfe was 

 recuperated by the rise of creatures not greatly differing 

 from squids and cuttle-fishes. They are generally spoken of 

 as belemnites — a name derived from the dart-Hke appearance 

 of their sheUs {BelemnitidcB). The shell, in being straight and. 

 tapering, exhibited a notable difference from the ammonite 

 sheU. It had, moreover, by a reverted extension of the mantle 

 or body-skin, become internal. 



Triassic belemnites were few in number, and smaU in. 

 size— the largest not being more than a few inches in length. 

 As a rule they were provided, hke cuttle-fishes, with ink-sacs,, 

 for clouding the water and confusing foes. 



The origin of the animals is lost in obscurity. Their nearest: 



