The royal natural history . the oldest and mostwidely distributed of all known organisms, being found from Silurian times throughall subsequent strata. The living R. psittacea shows best the characteristic beak-like process of the ventral valve ; the aperture for the stalk being found under thisbeak. The valves are fastened together as in the Terebratididce, but the calcareousframework consists merely of two short, narrow plates, which ai*e attached tothe smaller valve. Rhynchonella is not very numerous in northerly regions,but empty valves are found in mud. Observations on the living animal a
The royal natural history . the oldest and mostwidely distributed of all known organisms, being found from Silurian times throughall subsequent strata. The living R. psittacea shows best the characteristic beak-like process of the ventral valve ; the aperture for the stalk being found under thisbeak. The valves are fastened together as in the Terebratididce, but the calcareousframework consists merely of two short, narrow plates, which ai*e attached tothe smaller valve. Rhynchonella is not very numerous in northerly regions,but empty valves are found in mud. Observations on the living animal arerendered difficult by the fact that it is peculiarly sensitive to all disturbance,and closes its valves at the slightest movement. The arm - spirals widensufficiently to allow the cirri to reach the edge of the shell; the arms do notappear capable of unrolling and protruding beyond the shell. The members ofanother family of this order of hinged Brachiopods, the Sjnriferidte, are rendered LAMP-SHELLS. 43i Hingeless UPPER VALVE AND ANIMAL OK Crania (magnified). very remarkable by the long, spirally-coiled and calcified arms. Spirifer wasvery abundant in the Palaeozoic epoch, but died out with the Lias. The second order of the Brachiopods (Ecardines), or those whoseshells are without hinges, consists of but four families, two of whichmay be briefly described. The unstalked genus Crania is widely distributed,both geologically and at the present time. Its structure is so peculiar that itforms a family by itself (Craniida>). The shell is attached to some submarineobject by the ventral valve ; the dorsal valve is lid-like, and the two valves connected, not by a hingeor interlocking processes, but simply by muscles. Thebest-known of the four living species (here figured) ofthe northern seas, is almost always found in companywith Terebratidina, which, however, it does not followinto the seas of Northern America. The last family to be described, the Lingididce,is also one of
Size: 1712px × 1459px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
