PTEROPODA. 3 



6. Hyalea Planci, Lesueur, Ann. Mus. xv. {Planchus Min. Conch. 



t. 2, f. 6, g, h, i), is also a Biloculina. 



7. Dentalium trachea, Montague^ which has been formed into a 



genus by various authors, under different names, — as Ccecum 

 {Fleming), Brochus {Browne), Odontidium {Philippi), Ca;calium 

 {Macgillivray), Odontostoma {Cantraine), Dentalopsis {Clarke), 

 Odontina {Zhorzewsky), — has been doubtfully referred to this 

 order by M. Philippi {Moll. Sicil. 102). It has lately been 

 proved by Mr. Clarke {Ann. and Mag. Nat. Hist. 1849) to be an 

 operculated Gasteropode which will form a new family, which 

 may be called Ccecidce, among the division of the Ctenobran- 

 chiata. 



8. CuDULUs, Philippi, probably belongs to the same group. 



9. Dentalium Gadus, Montague, quoted as the genus Gadus by 



Rang ^ D'Orhigny {Voy. Amer. Alerid. Moll. 75), and referred 

 to the genus Creseis by Rang, appears to be a true Dentalium. 



Synopsis of the Orders and Families. 



Order I, Thecosomata. Body inclosed in a shell. Head not dis- 

 tinct. Wings 2, on the side of the mouth. Gills internal. 



Sub-order I. Animal and shell straight. Operculum none. 



Fam. 1. Cavolinid^. Shell calcareous, globular and conical. 

 Animal without any foot-like appendage between the fins. 



Fam. 2. Tripterid^. Shell calcareous, subcylindrical or conical. 

 Animal with a foot-like appendage between the fins. 



Fam. 3. Cymbuliad^. Shell cartilaginous. 



Sub-order II. Animal and shell spiral. Operculum spiral. 

 Fam. 4. Limacinad^. Animal spiral. Shell spiral, sinistral. 



Order II. Gymnosomata. Body naked. Head distinct. Wings 2 

 or 4, on the side of the neck, with an intermediate foot-like ap- 

 pendage. Gills external. 



Fam. 5. Clioneid^. Head with 6 conical tentacles. Fins 2. 

 Fam. 6. Pneumodermid^. Head with 2 disk-bearing arms. Fins 2. 

 Fam. 7. Cymodocid^. Head simple. Fins 4. 



b2 



