330 



LOWER INVERTEBRATES. 



papalts, which has each whorl of the spire crowned with knobs, and tlie small colored 

 si)ots of the shell much more irregular in shape and distribution than in 31. ejiiscopalis. 

 TIic genus Jlitra contains over two hundred species, a lai'ge proportion of which come 

 from tlie Philippines and the neighboring seas. Almost all of the genus are tropical 

 and seniitro])ical ; several being found in the West Indies; but an exception to this 

 distribution is found in 31. f/rdnlandica, as its name indicates, an Arctic form, which, 

 on account of peculiarities of its lingual dentition, has been separated as a sub-genus 

 Vblutomitra. 



The family Mueicid^, as at present limited, embraces a heterogeneous assemblage 

 of forms'. Several attempts have been made to divide it without doing violence to 

 the affinities of one or more genera, but no scheme has as yet received universal acceis- 

 tance. If we base the division on the lingual dentition, it does not agi-ee with char- 

 acters derived from tne animal and from tlie shell ; if on the anatomy of the animals, 

 still other features are not in accord, etc. With this uncertainty it is best, at least in a 

 popular work, to leave the classification in its ]jresent condition, and to define the 

 family as embracing a group of molluscs, in which the foot is broad and of moderate 

 length, the siphon long, the eyes at tlie base of the tentacles, while tiie characters derived 

 from the shell are the presence of a long or short, straight, anterior canal, and an oval 

 operculum with the nucleus at the smaller end. Necessaiily where so much con- 

 fusion exists thei'e will be an inequality in the relative rank of certain of the included 

 types, and in the following remarks some genera named will possibly not be worthy of 

 generic rank, while others, on the other hand, may deserve to be regarded as really 

 of the grade of sub-families. The same troulile also occurs with the next family, the 

 Buccinida;. 



The first sub-family, the MuriciiKc, is well marked by characters derived from the 

 shell. The growth is apparently marked by jjeriods of rest, and at each of these the 

 aperture is thickened and marked by ornamentations of various kinds. Then the shell 

 grows again, and shortly another period of rest ensues, when the nodes, spines, or 

 thickenings (\'arices they are called) of the mouth are repeated. These interrujitions 

 occitr at varying intervals in different sjiecies, and are of some use in defining 

 generic limits. A similar process occurs in some 

 othej- families. 



The typical genus is Miti-e.i; in wliicli the canal 

 is long and straiglit, the aperture round, and tlie 

 shell is interrujited by varices and spines at least 

 three times in tlie course of the growth of the whorl. 

 In the colder waters the colors are subdued, and the 

 shell does not acquire that fantastic form that is fre- 

 (pient in the tropical species. Tiie species are among 

 the most rapacious of molluscs, boring through tlie 

 shells of other s]>ecies in the same way as does the 

 Natica, to be descril^ed on a subsequent jjage. In 

 Enrojie, 3Iurex erinaceus does great damage to the 

 oyster beds. Allied sjiecies {31. brandaris and 3f. 

 trunczdus) were employed by the ancient inhabitants 

 of Syria and Greece in the preparation of the cele- 

 brated Tyrian purple. Of the two hundred and odd s|iecies of this genus, we need 

 only mention, in addition to those just referred to, the 3Iurex tenuispina, in which the 



Fig. 412. — Miirex endiva. 



