294 MELANIINiE. 



These animals are fluviatile, being inhabitants of fresh- 

 water lakes and rivers throughout the warmer parts of the 

 world. The apex of the spire is often eroded by the 

 action of the water in which they live. In the British 

 Islands they only occur as fossils; in the southern States 

 of North America they are numerous, and form peculiar 

 groups ; those with the many-whorled operculum appear 

 to abound most in the Old World ; in some instances 

 these animals are viviparous. 



Sub-fam. MELANIIN^. 



Operculum ovate and subspiral, or subcircular, and of 

 few whorls. 



Shell covered with a dark, horny epidermis; aperture 

 usually simple in front, without a distinct notch. 



Genus TIARA, Bolten. 



Shell ovate ; spire and aperture of nearly equal length; 

 whorls coronated with spines or tubercles ; aperture ovate, 

 entire in front, pointed behind ; inner lip very thin ; outer 

 lip simple, acute. 



Syn. Spirilla, Humph. Melas, Montf. Melacantha, 

 Swains. Amarula, Sow., jini. 



Ex. T. amarula, Linriceus, pi. 31, fig. 3. Operculum, 

 T. acauthica. Lea, fig. 3, a, 3, b. Shell, T. amarula, 

 fig. 3, c. 



This group comprises the ovate forms of the MelaniinoB, 

 in which the whorls are spinose ; they are either smooth 

 and black, covered with a villose epidermis, or trans- 

 versely striated and variegated. 



