FRONT-GILLED GROUP 3341 



variation of its color markings. C. cervus, C. adamsoni, C. thomce, C. nobilis, C. deles- 

 serti, are some of the most highly treasured, but the celebrated C. gloria-marts, 

 from the Mollucca and Philippine islands, of which only about a dozen specimens 

 are known, is still considered the finest shell of all, and a full-grown specimen in 

 good condition would probably now realize from two hundred to two hundred and 

 fifty dollars. Some, such as C. betulinus and C. suratensis, are extremely solid, but 

 a few, C. geographus and C. tulipa, are very thin. It has been asserted that certain 

 species have no operculum, but this is now believed to be incorrect. This struc- 

 ture is small, horny, narrow, and, being much smaller than the aperture of the shell, 

 in no way serves the purpose of defense. A large number of fossil species have been 

 described from the Tertiary formations. Some instances are on record of persons 

 having been bitten by cones when handling them, and it is said that the bite, to 

 some extent, is poisonous, but whether this characteristic is peculiar to a few, or 

 common .to all the species, we have no means of knowing. 



The auger shells, Terebridce, have a very different appearance to the cones, 

 and conchologically do not exhibit any particularly close relationship; although the 

 characteristics of the dentition certainly indicate their approximation. The mol- 

 lusks of this family have a small head with two small cylindrical tentacles, with 

 minute eyes at the tips. The foot is small, rounded in front, and elongate behind, 

 and supports a small, oval, horny operculum, with an apical nucleus. About two 

 hundred and thirty species have been described. They abound in tropical regions, 

 but a few occur in more temperate localities, such as Japan, California, and New 

 Zealand. Some of the shells are so solid (Terebra maculatd), and others so 

 extremely elongated ( T. pretiosa, etc. ) , that it would appear impossible for the 

 animals to carry them erect. Probably, in these instances, the shells are dragged 

 along resting upon the surface of the sand. They are all elongate in form, with 

 a small aperture, notched in front for the passage of the siphon. The whorls are 

 flat and generally divided below the suture by a spiral furrow. They are longi- 

 tudinally fluted, smooth or noduled, and it is upon these differences in sculpture 

 that the various subgenera are founded. 



The third family Pleurotomidce contains an enormous number of species, 

 certainly more than a thousand having been described. They are mostly small, 

 and show great variety in form. The species of the typical genus Pleurotoma are 

 spindle shaped, that is, have a long tapering spire at one end, and a prolonged 

 beak or canal at the other, and the outer lip has a distinct slit somewhat below 

 the suture. In Surcula and Drillia the slit or notch is at the suture, in Beta it is 

 indistinct. Some forms, Clavatula and Pusionella, have a semiovate operculum, 

 with the nucleus lateral; in Pteurotoma, Drillia, etc., it is ovate pyriform, with a 

 terminal nucleus; while in Mangilia, Cythara, etc., it is altogether absent. Colum- 

 barium, containing only a few species, is remarkable for the great length of the 

 anterior canal, and the spine-like ornamentation of the whorls. C. pagodoides, 

 dredged off Sydney in four hundred and ten fathoms, is one of the most beautiful 

 of all the family. All degrees in the length of the canal are observable, until we 

 find it reduced to a mere notch at the base of the aperture. Pleurotomidce exist in 

 every sea, but certain groups are more characteristic of cold and temperate climates. 



