266 Contribution to our knowledge of Pelagic Mollusca. [No. 4, 



Hyalsea tridentata, G-mel. PI. xxi, Fig. l. 



Anomia tridentata, Gmelin ; Forskahlii, Chemnitz ; Chiaje. 



Cavolina natans, Abilgaard ; Cavier. 



Caulina natans, Poli. 



Hyalsea papilionacea, Bory de St. Vincent ; Blainville. 



Hyalsea cornea, Roissi, Lamck. 



Hyalsea tridentata, Bosc; Lamck. ; D'Orbigny ; PhilippL 



Hyalsea Chemnitziana, Peron et Lesueur. 



Hyalsea Forskanlii, Les. : D'Orbigny. 



Hyalsea tridentee, Voyage Bonite, Moll. 



Hyalsea truncata Krauss. 



Shell semi-spherical, inflated, gibbous anteriorly, lateral points some- 

 what convergent, widely cleft, lateral margin of dorsal plate wrinkled, 

 slightly reflected, inferiorly five-ribbed, terminal tooth longer than 

 the lateral ones. 



Habitat. Indian and Pacific (?) Oceans. 



Hyalsea tenioforanchia, Peron, pi. xxi, Fig. 2. 



Hyalsea Peronii, Rang. 



Shell sub -triangular, flat, semi-transparent; lateral points wide, some- 

 what divergent ; upper third of cleft overlapped by margin of dorsal 

 plate, lower third overlapped by ventral margin ; inferiorly, three ribs 

 converge separately and narrowing unite towards the long terminal 

 tooth. 



Habitat. North Atlantic. 



Hyalsea affinis, <FOrb., pi. xx; Fig. 3. 



Hyalsea affinis, Desh. in Lamck. Hist. 

 (?) Hyalsea Peronii, Les. 



Shell ovoid, inflated, transparent, horny; inferior lip very long, nar- 

 row, sinuated superiorly.; inferiorly three ribs unite in anterior half 

 of dorsal plate, and thence descend posteriorly in one more or less pro- 

 minent rib. 



Habitat. Indian and Pacific Oceans. 



