ON 
RHYNCHONELLA ACUTA 
AND ITS 
AFFINITIES. 
Ove of the most remarkable fossils assumed to be distinctive of a 
particular geological horizon, and which, from its very striking out- 
line, most readily impresses itself upon the mind, is the Rhynchonella 
acuta of the Lias-marlstone, a Brachiopodous shell common at 
Stinchcombe, Churchdown, and other localities of this district, and 
well known elsewhere. Having paid considerable attention to the 
class to which it belongs, I have long abandoned the common practice 
of placing in the cabinet only those specimens which chance to accord 
with the forms figured and described as typical. Instead of doing 
this, I have selected, as good examples, those which manifestly have 
not been crushed or injured prior to their entombment and petri- 
faction ; and these I have arranged in series illustrative of specific 
development. 
This mode of procedure has taught me that the species under 
consideration assumes forms varying from that under which it is most 
generally known; and it has led me to believe that several so-called 
species of various authors are, in reality, mere varieties of this. 
All who have attentively studied the numerous Terebratulide of 
the Cotteswolds will have experienced the difficulty of assigning 
satisfactorily certain anomalous forms, occuring in beds ranging 
vertically from the Pisolite, or even lower, to the Cornbrash, to such 
well-established species as Terebratula mazillata, T. perovalis, T. 
globata, or T. intermedia, and will remember the remarkable 
varieties of individual character presented by other species, as, 
for example, T. plicata, T. simplex, T. fimbria, and T. carinata, 
sufficiently striking when studied in solitary examples, but, in an 
