48 



SCALARIA.^CYCLOSTOMA.— VALVATA. 



equatorial regions of the Atlantic Ocean. It is a common^ 

 heavy shell ; it has a horny operculuni, and is remarkable for a 

 tooth situate at the orifice of the umbilicus. 



33. The Delphinula has a thick shell like the last, but rolled 

 almost in the same plane, and the aperture is entirely formed 

 by the last whorl of the spire (J?^. 45): ' 

 the most common species is remarkable 

 for its twisted and' branching spines. 



34. The TuRRiTELLA and Scalaria 

 have a very elongated spire : in the first 

 {Jig. 33, page 44),. the mouth or aper- 

 ture of the shell is formed as in the 

 Turbo, properly socalled, a^nd in the last, 



it is similar to that 

 of the Delphinula. 



Fig. 4.5. DELPHINULA. 



-a 



The Wentletrap or 

 Precious Scalaria {fig- 46) has the volu- 

 tions connected by longitudinal ribs. 



35. The Cyclostom.e, which are dis- 

 tinguished by the absence of branchiae, and 

 by their aerial respiration, also have a shell 

 with a round mouth, 

 closed by a thin circu- 

 lar operculum {fig. 47, 

 6) ; it is in form of an 

 oval spire, and finely 

 striated transversely. — 

 These animals live in 

 woods, under moss and 

 Fig. 46. — SCALARIA. stones. 



36. Finally, the fresh-water mollusks, named Valvata, — in 

 which the shell somewhat resembles that of the Planorbis,. but 

 has a circular aperture,, furnished with an 

 operculum, — ^also take their place here. One 

 species, which inhabits stagnant waters in 

 France, has been called the feather hearevy 

 from the manner in which the branchia, which 

 is in form of a feather, is protruded and floats 



Fig. 48. ^^ ^he surface of the water when the animal 



VALVATA. wishes to breathe. 



Fig. 47. 



CYCLOSTOMA. 



3.3. What are the characters of the Delphinu'la ? 



.34. What are the characters of the Turrite'lla and Scala'ria ? 



35. What are the characters of the Cyclo'stomoe ? (Cyclostoma : from the 

 Greek, kuklos, round, and stoma, mouth, — round-mouth.) 



36. Wliat animals belong to the genus Valva'ta ? (Valvata, Latin, formed 

 from valv<2, folding doors). 



