194 Mr. W. Clark on the British Trochus Cutlerianus. 



that my T. Cutleriunus cannot be the T. exilis of Philippi, and 

 establishes the mistake of Mr. Jeffreys. I might here close my 

 case ; but in corroboration I proceed. 



The general form of the T. exilis tapers from the globose 

 body-volution, with/owr others, to a subconic pointed termina- 

 tion ; mine, from the subglobular basal whorl, cannot be said to 

 taper at all, but suddenly subsides into a flattish, blunt, irregular 

 coil of hardly two turns. 



The aperture in the T. exilis in the text is called suborbicular, 

 and the figure explains the character of that term by portraying 

 a regularly curved and perfectly even apertural periphery ; but, 

 in the British and perfect examples of the T. Cutlerianus, the 

 aperture presents two conspicuous sinuations (it is never without 

 them) — one at the base, and another at right angles about the 

 middle of the outer lip, which sinuations or indentations, under 

 adequate optical assistance (which, in so minute an object, should 

 be a powerful Coddington lens), exhibit an apertural periphery 

 of a subquadrangular instead of a suborbicular form. 



It is useless to continue the comparison of two species so dia- 

 metrically opposed in every essential character. I challenge the 

 production of a British T. Cut leri anus iha.t departs from the distinc- 

 tions I have enunciated. As to size, ten years ago I stated that 

 my shell was " circa g uncise " in length and breadth ; but 

 the selection of the largest specimens from many hundreds cap- 

 tured by myself, and accurately measured, has proved that in no 

 instance has it ever reached j jth of an inch, either axially or 

 transversely ; and I feel confident that no adult T. Cutlerianus will 

 ever be found to exceed these dimensions, or even to equal them. 

 I may state that the presence of the sinuations of the aperture is 

 a true test of a T. Cutlerianus being full-grown ; and that shibbo- 

 leth never fails to appear before it has reached gu^^ °^ ^^^ ^^^^ 

 diameter. 



The natural size given in the figure of Philippics single fossil 

 is at least twice that of the largest T. Cutlerianus. After this 

 comparison, can any intelligent observer believe that my shell, 

 that may be said not fully to complete three volutions, is Phi- 

 lippi's of five, and that the form of his shell represents mine ? 

 or that his i-egularly-curved even aperture is that of my object 

 with its curious sinuations, which, I repeat, are invarialjly pre- 

 sent in adult perfect examples ? Can we suppose that so excel- 

 lent an observer would have failed to mark the indentations in 

 his enlarged figure, if they had existed ? 



I conclude, and trust I have fairly demonstrated that the T. 

 exilis and T, Cutlerianus are most distinct species; and that, 

 agreeably to the conventional laws of naturalists, I am, by 

 priority of discovery, at least as yet, entitled to be considered the 



