164 JANTHINA. 



more flat ; lower extremity tridentate. — Obs. The singular struc- 

 tures composing this genus were formerly taken for bivalves, and 

 named Anomia Tricuspidata, &c. They are now known to belong 

 to the class of molluscous animals, called Pteropoda, from the 

 wing-shaped organs of locomotion. A species of Hyalsea occurs 

 in Sicily in a fossil state. Eecent species are found in the Medi- 

 terranean, Atlantic, and Indian Oceans. Fig. 226, H. Tridentata. 



HYALINA, Studer. Vitrina, Drap. 



HYALINE. {Hyalus, glass.) Glassy, thin, transparent — Ex. 

 Carinaria Mediterranea, fig. 488. 



HYDROBRANCHIATA. Bl. The first section of the order Gas- 

 teropoda, Lam. containing Molluscs which breathe water only ; 

 divided into the families Tritoniana, Phyllidiana, Semi-phyllidiana, 

 Calyptracea, Bullseana, and Aplysiana. 



HYGROMANES. Fer. A sub-division of Helix, containing H. 

 limbata, Auct. &c. Gray's Turton, p. 143. 



HYRIA. Lam. A genus composed of species of Nayades, dis- 

 tinguished by their alated dorsal margins, and lamellated lateral 

 teeth. South America. Hyria corrugata, fig. 143, Hyria Syr- 

 matophora, fig. 144. 



HYRIDELLA. Sw. A genus of " Hyrianse," Sw. described as 

 differing from Hyria, Auct. in having a cardinal as well as a 

 lateral tooth in each valve. Sw. p. 380. 



HISTRIX. Humph. Ricinula, Auct. 



JANERA. Schum. A genus composed of species of Pecten, 

 Auct. having oblique plicse or calli on each side of the ligamen- 

 tary pit. Ex. P. plica, fig. 1 72. Decadopecten, Ruppell. 



JANTHINA. Auct. (Janthum, a violet.) Fam. Neritacea, Lam. 

 Oxystomata, Bl. — Descr. Sub-globose, thin, fragile ; spire short, 

 consisting of few whorls; aperture angulated, at the anterior 

 junction of the inner and outer lips ; columella tortuous, con- 

 tiguous to the axis ; outer Up thin, sinuated in the centre. — Obs. 

 The shells composing this genus are celebrated for their beautiful 

 purple colour. The animal possesses a small vesicular process, 

 which keeps it floating on the surface of the water ; it exudes a 

 purple secretion when irritated. It is occasionally floated on to 



