TROCHUS— TURBO. 



47 



Fig. 41. TROCHUS CONCAVUS, 



Fig. 42. 



TROCHUS IRIS. 



Another variety is remarka- 

 ble for a deep excavation at the 

 base of the columella, resem- 

 bling an umbilicus, and a pro- 

 jection of the circumference, as 

 is seen in the figure of the con- 

 cave trochiis {Jig. 41), which 

 inhabits the Indian Seas, and is 

 considered rare. 



There are 

 other species, 

 without an umbi- 

 licus, conical with 

 a very oblique 



base ; the aperture large, slightly angular » the 

 columella twisted, and forming a kind of tooth at 

 its termination. Such is the rainbow trochus 

 {fg. 42), the nacre of which is a beautiful golden 

 green, with very brilliant reflections of red. 



31. The tribe of Turbo comprises all the pecti- 

 nibranch gasteropods which have a completely and 

 regularly turbinated shell, terminated by an entirely round aper- 

 ture In it we range the turbo 

 properly so called, delphinula, turri- 

 tella, scalaria, cyclostoma, valvata, 

 &c. {fg. 43). 



32„ The Turbos properly so 

 called are recognised by their round 

 or oval thick shell, in which the ap- 

 erture is completed within by the 

 whorl of the spire next to the last. 

 These mollusks have two loner ten- 



o 



tacles, which, 



at their base, 



externally, 



support the pedunculated eyes ; on the 



sides of the foot we remark membranous 



wings, sometimes simple, sometimes fringed 



or furnished with one or two filaments ; 



and their operculum is sometimes horny, at 



others calcareous, or extremely thick.— 



Among the varieties of this genus is the 



Tvrho Pica {fig. 44), which inhabits the 



31, What are the characters of the tribe of Turbo ? (Turbo is a Latin 

 word, meaning a whirling or twisting.) 

 32 What are the characters of the Turbo properly so called? 



Fig. 43. — TURBO. 



Fig. 44. TURBO PICA. 



