316 
THE GEOLOGIST, 
Professor Quenstedt, in like manner, in liis recently-piiLlislied 
"Jura," treating of R. bidens, Phillips, seems disposed to consider it 
and R. triplicata as varieties of R. acuta, distinctly pointing out their 
general resemblances ; although German authors generally agree in 
stating that this species does not occur in the Suabian Alps. 
Not to needlessly multiply quotations, I may yet briefly state that 
Davidson, in his Monograph on British Jurassic Brachiopoda, figures 
what he considers to be the R. hidens and R. triplicata of Phillips as 
varieties of R. variahilis, which he believes to range through the 
Lower and Middle Lias ;* but, unless his figures are taken from the 
original specimens of Professor Phillips (and these were very ill 
drawn by the last-named gentleman), I discover nothing in his obser- 
vations upon either species to modify the conclusions at which I have 
arrived from a comparison of the observations of all these authors. 
Labyrinthine as appears to be the confusion of ideas in the state- 
ments cited, the clue appears to me to lie within grasp. Let ns 
remember that the three forms, in one case, occupy the same zone, 
occasionally occurring together, at other stages or places one or other 
numerically preponderating ; that the diff"erence between R. acuta 
and R. bidens, in the opinions of authors and observers in every way 
entitled to respect, is no greater than between the latter and R. tri- 
plicata, being one of degree only and not of kind. The suggestion, 
therefore, naturally arises that they may really pertain to one species. 
Assuming that we are justified in arriving at this conclusion, all 
difficulties vanish. We simply learn the not uninteresting facts in its 
natural liistory — that the geogi-apliical distribution of one of the most 
characteristic shells of the stage to which it belongs was co-extensive 
with that of many of its usual companions, from which it would 
otherwise appear to be somewhat unaccountably separated ; and that, 
in particular portions of the area which it occupied, it attained to 
degrees of development denied to it in others. 
Having pointed out instances of the confusion of these varieties with 
species of lower stratigraphical range, I will now direct attention to 
one instance of R. bidens having been recorded as occurring in a bed 
higher than that in which it is usually looked for. 
* In this monograph, Mr. Davidson gives his reasons from considering R. bidens 
and its synonym R. trijilicata.as specifically different from R. acuta. His statements 
on this sulijcct .should be referred to. — Ed Geol. 
