TROCHUS TURBO. 



47 



Fig. 41. TRCCHUS 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 trochus (fg. 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 i 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 long ten- 

 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 

 Tvrbo Pica (fg. 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. 



