Genus Latirus. 381 



them for purposes of protection. This seems not an 

 improbable theory. 



(VIII.) On Latirus cingulatus (Lam.). — This extra- 

 ordinary, though not infrequent species, is not so isolated as 

 would at first sight appear. The solid angularity of its 

 uncouth whorls,and great extension of the outer labial tooth, 

 distinguish it at once. It was originally placed by Lamarck 

 in his genus Monoceros, with certain Purpuroid shells which 

 are, likewise, ornamented with a more or less conspicuous 

 tooth. Finally, Dr. J. E. Gray made it the type of his 

 genus Leucozonia^ having discovered its true affinities. The 

 columellar plaits are well developed ; the dentition is pre- 

 cisely that of Latirus. As to be noticed in the remarks 

 concerning the sequence here adopted, I have transposed 

 this shell, with the other Leiicozonice^ to Latirus proper: — 

 there are signs of the labial tooth in several of the allied 

 forms, and Latirus amplustris^ though untoothed, has inti- 

 mate affinity in other ways with cingulatus. 



The species is littoral, living on rocky coasts of Western 

 and Lower California, Mexico, to Panama, the Rev. P. P. 

 Carpenter, Prof C. B. Adams, and other collectors having 

 noticed it in many places. Specimens are almost invariably 

 covered with nullipores and other growths, rendering them 

 most unsightly till these are removed. What the use of the 

 labial tooth can be is mere conjecture. It cannot be for 

 purposes of spearing or securing its prey — a Molluscan 

 Narwhal — nor for digging food out of the recesses of 

 the rocks, for it is not placed in such a position as to give 

 the shell any leverage, and, moreover, were it of any use, we 

 might expect to see in it signs of wear and tear, epecially in 

 old specimens, (I have one aged well-grown form with the 

 tooth ^ inch long), but it always looks sharp and strong 

 in any shells that have been procured alive. 



The shells of the subgenus Cerostoma of Murex (L.), 

 also Monoceros (Lam.), and Chorus {(jXd.y\d\\ possess a similar 

 tooth, but in none is so high or typical a development 

 reached as in Latirus cingulatus (Lam.) 

 X 



