CLASS III. BRACIIMPODA (q.v.). Body protected by a bivalve shell lined by au integument or mantle. Mouth furnished with spirally coiled processes or arms. Ven tral valve usually the larger of the two. All marine; commonly known as lamp-shells. See LAMP-SIIELL. This class is divided into ten families.
Avidly 1. Threbratulidee (Lat. terebro, to bore). See TEREBRATULA. Most of these mollusks commenced their existence in the paleozoic rocks, and hitve survived to the present time, but some are extinct.
Family 2. Thecidide (Gr. the/a', a sheath). These animals are attached to some object at the sea-bottom by the beak of the ventral, or larger valve. All the known species are included in the single genus thecidium, which commenced in the upper trios, and there is only one species which is not exclusively fossil.
Family 3. Spiriferide. See Sri]ImEits. These animals had a curiously constructed shell, and their remains are very interesting. They range from the Silurian to the Permian formations, and none have been found later than the lias.
Family 4. Koninchinida. The only genus known, koninckina, is represented by a single species, K leonhardi, of the trigs of St. 5. Rhynchonellida (Gr. rhynchos, a heak). Commencing in the lower silurian, one genus only remaining, rhynchanella (q.v.). The (q.v.), an interesting fossil, ranges from the lower silurian to the carboniferous inclusive.
Family 6. Sirophomenide. All exclusively paleozoic. Principal genera: Orth orthisina, Da•idsoula, strophomena, and leptama. Sec °Ifni's. The typical species of orthisina are siltirian; but according to Davidson the genus ranges through the Devo nian and carboniferous formations into the Permian.
Family 7. Product/dm. Shell attached to submarine objects by the beak or by means
of spines borne by .the ventral valve. Genus chonetrs, found in sillirian, Devonian, and carboniferous formations. Producta in Devonian to Permian.
litorily 8. Craniada This family contains only one genus, crania, which is found in the silurian and in all formations to the present time. Toe fossils are very beauti ful and interesting.
Family 9. Disci/dam. Range from Silurian to present time. A description of these interesting fossils may he found in the Paleontology of New York, by James Hall, and in Dana's Ira nual of Geology.
Family 10. Lingulida (Lat. lingula, a little tongue). Range from Cambrian period to the present time. Animal fixed by a muscular peduncle passing out between the beaks of the valves. Shell of horny texture, containing phosphorus in its composition. The genus ()bolus, a beautiful fossil, is confined to the silurian rocks. The present representa live is lingula (q.v.).
Divisiox B. MOLLUSCA PROPER. Those members of the sub-kingdom mollnsca which have three principal pairs of ganglia, distributed irregn hilly in position. and a heart which never has less than two chambers. They are naturally disposed into two groups—the Acephala, which have no distinct hoed, as the oyster and other lamelli branchiata; and the Encephala, in which there is a distinct head, as in the gasteropods, pteropods, and cephalopods. These three latter groups or classes have complicated arrangements of teeth upon the tongue, for which reason they have been given by Huxley the general name odontophora. The division acephala contains only one class.