- Tridacna gigas.
- T. squamosa.
- T. elongata.
- T. crocea.
- T. mutica.
- T. serrifera.
- T. pustulosa.
2. Genus Hippopus. Pl. [VIII].
Animal. As above.
Shell. More elongated and inequilateral than in the Tridacna, the anterior side being longer than the posterior; the posterior slope closed with a dentated margin. Inhabits the Indian seas. One species.
- Hippopus maculatus.
FAMILY XVI.
Mytilacea. Three genera.
1. Genus Mytilus. Pl. [VIII].
Animal. Body oval, somewhat inflated; mantle open in its inferior half only, and terminated posteriorly by an oval cleft with fringed edges; a linguiform, canaliculated, abdominal appendage, with a byssus at its base behind, and several pairs of retractile muscles; mouth with simple lips; two contractile muscles, of which the anterior is very small.
Shell. Of a serrated tissue, elongated, more or less oval, sometimes subtriangular, equivalve, summits anterior, more or less curved, sloping inferiorly in a slight degree; hinge toothless, or with two very small rudiments; ligament dorsal, linear, subinterior, inserted in a narrow and very long furrow; two muscular impressions, of which the anterior is very small, besides those of the retractile muscles. Inhabits the British and American seas. Forty-two species.
- Mytilus erosus.
- M. decussatus.
- M. elongatus.
- M. Zonarius.
- M. violaceus.
- M. smaragdinus.
- M. edulis.
- M. Hesperianus.
- M. exustus.
- M. ovalis.
- M. Domingensis.
- M. Afer.
- M. ungularis.
- M. borealis.
- M. augustanus.
- M. lacunatus.
- M. incurvatus.
- M. abbreviatus.
- M. Magellicanus.
- M. crenatus.
- M. hirsutus.
- M. latus.
- M. ungulatus.
- M. opalus.
- M. corneus.
- M. retusus.
- M. perna.
- M. bilocularis.
- M. ustulatus.
- M. Senegalensis.
- M. achatinus.
- M. planulatus.
- M. Galloprovincialis.
- M. lineatus.
- M. canalis.
- M. sanguineus.
- · · · · ·
- M. hamatus.*
- M. croceus.*
- M. cubitus.*
- M. lateralis.*
- M. Californianus.*
- M. leucophœatus.*