118 GENUS XXVI. mVREX. 



as in Ricinus ; and sometimes of an irregular figure, as Anus ; 

 also it frequently has teeth on one or both sides, though some- 

 times it is without any. 



The outer surface of these shells is genei*ally rough, with 

 ridges, tubercles, or spines. Many species seem to have a 

 periodical growth ; they appear at certain times to cease grow- 

 ing, when they thicken the outer lip, and form the teeth at 

 the aperture : the mouth is then said to be completely formed : 

 after a certain time they grow again, and form another mouth, 

 as before : the distance between varies in the different species. 

 The ridge where the former mouth was formed is then called 

 a suture ; the distance between the sutures is in many species 

 two-thirds of the circle; in some it is only one-half of the circle; 

 in other species more, and in some less. These sutures are 

 found also sometimes in other genera, as in tlie second divi- 

 sion of the Buccina, but not so general in any as the Mwrex. 

 In some species these sutures are smooth, as in 31. Tritonis, 

 Vertagus, &c. ; but in more they are rough with tubercles, as 

 in M. Gyrimfs; some are rough witli spines, asM.Rana; 

 in others they extend into foliations, as M. ra?nosus. 



From the number and variety of the shells which are placed 

 in this genus, it is become almost impossible to distinguish a 

 Murex from a Ruccinum on the one hand, or from a Strombus 

 on the other ; so that, if Lamarck's arrangements are not 

 adopted, still there appears to be a necessity for forming some 

 new genera. The essential character of the Ruccinum, Strom- 

 bus, and Murex, being a canal either straight, or bending to 



