the Caribcean Islands. 541 



Tab. Supp. xxviii. Fig. 4. Animal supinum, a Operculum, 

 b Sipho dexter, c Sipho respiratorius. — 3. Idem serpens. — 6. Alae 

 cervicis. — 7. Operculum. 



There are probably several species confused under the name 

 of Planorbis cornu arietis : according to Gmelin one is an in- 

 habitant of China. My friend Mr. Swainson, in his incompar- 

 able Zoological Illustrations, Vol.11, pi. 119, (never having seen 

 the operculum of the PL cornu arietis of Lamarck,) has ob- 

 jected to Mr. Sowerby's retaining it in the genus AmpuUaria. 

 This learned zoologist, who, with his masterly pencil, has done 

 so much to illustrate these shells, in a subsequent part of his 

 work, mentions that the operculum had at last been made 

 known to the European naturalist, and very properly advises 

 that it should be retained as the terminal species of the Ampul- 

 larice. To Planorbis it cannot possibly belong. 



Fam. OsTREAD^. Guild. 

 Gen. OsTREA. Auctorum. 



Char. Gen. 

 Animal. Corpus complanatum, pallio obvolutum. Pallium 

 contractile, bipaginatum, superne clausum, margo posticus liber, 

 serie duplici teiitaculorum, Braiichia fere longitudine corporis, 

 latae : fimbriae quatuor, plicatae, subcontractiles, duae in utroque 

 latere. Appendices frontales quatuor, compressi, lanceolati, ex- 

 terne venosi, interne branchiis similes. Musculus clausoriiis sub- 

 centralis, compositus, divisio inferna sublunata. Abdomen ar- 

 cuatum. Rectum longissimum, liberum. 



Testa foliacea, irregularis, inaequivalvis; umbonibus (testae 

 clausae) disjunctis, aetate inaequalibus. Valva inferior major, 

 concava, adhaerens; umbone producto, subcanaliculato. Superior 

 minor planiuscula, operculiformis. Cardo edentulus. Ligamen- 

 tum medium, subinternum, breve, ad basin umbonum in fossula 

 cardinal! affixum. Impressio muscularis unica. Basis tenera 

 foliacea. 



