GASTROPODA. 961 
Lophospira.] 5 
counted 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 
numerous 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 
trouble recognize them. 
As far as known Lophospira ranges from the Calciferous to the Hamilton group, 
in other words 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 
Measures (see p. 952) so greatly resemble the average Lower Silurian types of the 
genus that it is difficult to escape the conviction that they are direct descendants 
of them. Worthenia, though sufficiently distinguished by having an apertural slit, 
might 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 
(ihlert 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 hight of the spire and the whim of the author, under either 
Murchisonia or Pleurotomaria. 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 
strikingly shown by the figures on plates LXXII and LXXIII. Take for instance 
various species of the Bicincta section, beginning with L. humilis Ulrich, the spire 
of which is so low that according to methods prevailing heretofore no one would have 
hesitated in placing it as a Plewrotomaria. From this it is certainly not a great step 
to reach L. bicincta Hall which Lindstrém calls a Pleurotomaria, while American 
authors generally have referred it to Murchisonia. Next we have L. concinnula U. 
and 8. and L. jillmorensis U. and 8., in which the spire is higher, and finally L. 
procera Ulrich in which it is very much higher than in L. humilis. Fully as great 
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