156 



surface is convex and smooth, as in the several species 

 just described ; from all of which, except T. platyloba, 

 (which is known by its flatness,) it is distinguished by 

 the lateral plaits. 



All the figures are of specimens from Ireland, except 

 fig. 6, which is taken from one found in Derbyshire. 



Were it not that we possess the individual specimen 

 Mr. Martin figured, we should, notwithstanding the ac- 

 curacy of his figure, have been in some doubt regarding 

 its identity with the species before us ; but we find its 

 blunt form to arise from distortion, caused by several very 

 evident fractures. Terebratula lateralis M. C. (tab. 83, 

 f. 1,) is probably a variety of T.Pugnus, although it have 

 only three plaits : however, the difiiculty of distinguish- 

 ing which are species, and which are varieties, is so 

 great in this variable division of Terebratulae, that I can- 

 not speak positively. Figs. 3, 4, and 5, upon the present 

 plate, are very nearly related to T. platyloba upon the 

 last plate, and seem to point out that as a variety only of 

 T. Pugnus. The number of plaits, the form and general 

 aspect even, is so inconstant, that out of several hun- 

 dred specimens hardly two can be found alike. Those 

 with lateral plaits are the most variable, and might per- 

 haps be divided into more species ; but it would be diffi- 

 cult to assign the boundaries. On the other hand, the 

 T. inflata is in general recognised immediately by its 

 form. 



In the Encyclopedic Methodique (tab. 245, figs. 6 and 

 7) are figures of a Terebratula with lateral but no cen- 

 tral plaits. Can this be a variety of either of the Irish 

 species ? 



