THEORY OF R U5ICAX3 LSD MORPHOLO :'.l 



differ but little at any age. The four tained 



throughout life, and have comparatively simple margins. The adult, however, 

 similar to ■ true larval form except in the Barae Bense that an old whorl is 

 simihu rn young, <>r 1 1 1 * • toothless gums of an old man are -miliar to the 



• tli appear. The Bnculites are not as i rule strictly 

 tubular whorls, as in the naopionic r Ammonitinae, but are gener- 



ally more or less compressed in the adults, like the aged whorl coiled 



shells. The development skipped the normal prog of the proximate 



coiled ancestors, and, like Byphilitic children, these shells had no proper 

 adult - le, degradational characteristics while -till \ 



. purely nostologic forms. 

 Tin- l.iu of evolution !'<■. ns therefore t" be as follows: 



y 



. tcht il 



■ for the number of uncoiled Ammonoids in tin- Upper Cre- 



-. their wide distribution, ami tin 1 undeniable fact, that they were the 



members of an order then rapidly in :tinction, unless we imagine the lt« n- 



eral ■ iring this period to have become unfavorable. The 



ed in tin' i'": in- of tin' groups a- a whole similar modifi- 



1 by the unfavorable effects of the local surroundings i 



iint) other shells in more limited localities during tin- Jurassic period. 



I bifurcatus Bhells anil tin- uncoiled cretaceous Ammonoids arc not isolated 



individuals, — like tin- turrillitic deformitiesoi Ammonitinae figured by D'Orbigny 



under the nam '•' I ( . or the planicostan 



- figured in Cor. . I' III. 1 7-1".. ami the scalariform 



Planoi ii, or multitudes of similar instances known t,. ever) Btudent 



aera. These can <nil\ be 

 tli.- result of hereditary tendencies acting up 



ids of time mor less prolon 



t B S ol tin- < 



en us, but probably always polyphylettic 

 i B '■ »rth America have esemblance to those 



that th. allied species ; but there are 



in the peculiar nodular marking! >l many -i 



which to think that they originated from American si 



have common chai in the Butures, and 



in th- iid the abdomen, which 



with 1 M published in lii- Invert* 



imon chai I he suture rned, 



illv tin- i and length ol the first lateral lobes, hut hi 



/' '. which make tli- 



1/ l.\ I I I I 



' i 



