MITRID^E. 107 



designate them merely by numbers. The grouping of the 

 species by these two authorities is in many respects widely 

 different ; I have carefully compared them together, and with 

 the shells, and shall attempt to improve upon both. 



The Mitras have been monographed by Kiister, Kiener, 

 Reeve and Sowerby, the work of the latter being by far the 

 most recent and complete, embracing nearly five hundred species. 

 The " Thesaurus " was published in 1874, and since that date 

 some additional species have been described ; there are also a 

 number of species obscurely published or which, for some 

 other cause, appear to have escaped Mr. Sowerby 's attention, 

 so that in all the number of specific names which might 

 nominally hold place in the present work would not be far from 

 six hundred and fifty. The vast increase ol our knowledge of 

 specific variation developed during the past few years has, 

 however, induced a decidedly more conservative, and it is 

 believed, more philosophic, view of species, than that prevalent 

 only six years ago, so that I have been enabled to effect a vast 

 reduction in the specific ranks a reduction which will probably 

 become still greater as additional material is given to the 

 student 'for comparison. 



When irritated, some species of Mitra emit a purple fluid 

 having a nauseous odor. 



The genus is at present tropical and subtropical in distribu- 

 tion, but few small species being found in the colder latitudes. 

 Batli3 T metrically they range from low-water to eighty fathoms, 

 the smaller species being usually found along shore-lines. 



About a hundred fossil species have been described, 

 commencing with the cretaceous period. * M. G-rcenlandica, at 

 present confined to Arctic waters, is found associated with 

 M. cornea, a somewhat similar Mediterranean species in the latest 

 British Tertiaries. The Mitridae inhabit various stations ; many 

 being strictly reef shells, where they lurk in holes and crevices 

 under sea-weed, but are most generally concealed under 

 stones and blocks of- dead coral. Others burrow in sand or 

 sandy mud at various depths ; some delight in stony ground 

 inside the reefs, where they remain concealed under clumps of 

 coral during the day, and like the sand species are nocturnal in 

 their habits. 



