ON 



RHYNCHONELLA ACUTA 



AFFINITIES. 



ONE 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 RhynchoneUa 

 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 Terebratulidee 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 maxtilata, 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. fonbria, and T. carinata, 

 sufficiently striking when studied in solitary examples, but, in an 



