>TROPODA. '"'1 



Lopkoplr.) 



iinted among the common fossils at the localities where they occur. Moreover, 

 in our opinion, the species are comparatively constant and therefore easily disting- 

 uished, although in practice among collectors no group of species has been more 

 persistently thrown together as of one or two species than has the majority of the 

 mini. Moii- types which on the following pages we endeavor to distinguish in such a 

 manner that any one having good material at his command may without much 

 t roul ile recognize them. 



As far as known Loph*i>ira ranges from the Calciferous to the Hamilton group, 

 in other word* from the base of the Lower Silurian or Ordovician to the middle of 

 the Devonian system. However, by far the greatest development of the genus 

 occurred in the various groups of the Trenton period. That the genus extended 

 through the Devonian into the Carboniferous rocks is, to say the least, doubtful. 

 We come to this conclusion despite the fact that the Worthenias of the Coal 

 M.M- .:- -ee p. !i.V_'< -o greatly re-eml>le t he a\ .-rajje Lower Silurian type- of the 

 genus that it i- <litlicult to escape the conviction that they are direct descendants 

 of them. \\'<rthfnia, though sufficiently distinguished by having an apertural slit, 

 mi^'lit readily have acquired this difference through gradual development, but we 

 know absolutely of no intermediate later Devonian and Sub -Carboniferous 

 Lophospira-like shells from which they might have been derived. For the present 

 therefore, especially after considering that the apex of the shell of Worthenia is 

 blunt and the embryonic whorls rounded, we incline to the view that the Carbonif- 

 erous genus was evolved from some low-spired round-whorled shell like those which 

 (Khlert proposes to distinguish as Gyroma. Excepting the initial cell or turn, 

 which we have not seen, the apical whorls of Lophospira are not materially different 

 from those following. 



Many of the species now referred to this genus have heretofore been placed, 

 according to the bight of the spire and the whim of the author, under either 

 Mun-hisoni'i or rifurnt,,n,<iri<i. No genus is better calculated to show the unrelia- 

 bility, as a generic character, of the hight of the spire. This fact is we believe 

 -trikingly shown by the figures on plate- IAXII and IAXIII. Take for instance 

 various species of the Hii-inrl<i section, beginning with /. . Innnili.'i I'lrich, the spire 

 of which is so low that according to methods prevailing heretofore no one would have 

 hesitated in placing it . ,(.///./. From thi- it is certainly not a great step 



to reach /,. bicin<i,i Hall which Lindstrora calls a Pleurotomaria, while American 

 authors generally have referred it to Mu> . Next we have L. conrinniila U. 



and S. and L. tillmorensis U. and S., in which the spire is higher, and finally L. 

 proeera finch in which it is very much higher than in L. humili.t. Fully as great 



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