CHAF. IV. SUB-GENERA OF MITRA AND TIARA. 131 



to know to which of them a Lamarckian Mitra really 

 belongs. We are sorry, indeed, to impose so much trou- 

 ble upon collectors; but the blame,, if any, must be 

 laid upon Nature not us : for we merely endeavour to 

 trace her steps. But she does not stop here. Into each 

 of these sub-genera, which happen to be full of species, 

 she actually carries the same principles of variation ; so 

 that, if all the shells really belonging to our sub-genus 

 Mitra, even as now restricted, were spread before the 

 naturalist, he would find not very incipient characters 

 of every one of the sub-genera just enumerated ; and 

 this, to such an extent as to justify our reaching this 

 conclusion, that if the whole of the species that have 

 been created were known, every Mitra would have its 

 counterpart, or prototype, in the circle of Tiara. 

 Any naturalist may convince himself of this, by look- 

 ing to the five sectional types of the sub-genus Mitra, 

 for instance, as episcopalis, rujfina, punctata, lactea, and 

 sonata. The second represents Tiarella by its crenated 

 suture ; the third shows us the roughness of Scabricola ; 

 the fourth the effuse aperture of Nebularia; and the 

 fifth the dingy colour and thick epidermis of Strigatella. 

 The Mitra terebralts and the Tiara terebralis* are 

 counterparts of each other, and are only prototypes, 

 under a different form, of the genera Terebra and Tur- 

 ritella. We regret exceedingly that we cannot give as 

 full an exposition of the mitres as we have done of the 

 volutes : half a volume would hardly be sufficient. It 

 seemed preferable fully to detail our analysis of the 

 first, as being the typical group ; and because, from the 

 comparative paucity of the species, the natural series be- 

 came more difficult to demonstrate than that of the 

 mitres. Now, as the principle of variation in each is 

 precisely the same., we have given only the results of 



* Of this shell, Mr. Broderip justly observes, " It is one of the most slen- 

 der of its genus, and has very much the general character and form of a 

 Terebra : this resemblance is increased by the circumstance of its having 

 one spiral groove more deeply impressed than the others, placed at about 

 one third of the length of each volution before the suture." Proc. ZooL 

 Soc. part iii. 1835, p. 196. 



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