In certain forms, as in Terebratula and Terebratulina, it is short and simple, .and attached to a small divided hingeplate, the two riband-shaped lamina being bent upwards in the middle (fig.
The cardinal process is prominent, and on each side of the hinge-plate are situated the dental sockets; the loop in Terebratulina becomes annular in the adult by the union of its crural processes (fig.
Loop of Terebratulina caput serpentis.
In Terebratulina, Rhyn- chonella, Lingula, and possibly other genera, the arms can be unrolled and protruded from the opened shell; in this case the tentacles also FIG.
Blochmann in 1884, however, observed this organ in the living animal in species of the following genera: - Terebratulina, Magellania [Waldheimia], Rhynchonella, Megathyris (Argiope), Lingula and Crania (fig.
It consists of a definite contractile sac or sacs lying on the dorsal side of the alimentary canal near the oesophagus, and in preparations of Terebratulina made by quickly removing the viscera and examining them in sea-water under a microscope, he was able to count the pulsations, which followed one another at intervals of 30-40 seconds.
Conklin's on " Terebratulina septentrionalis " (P. Amer.
No stalk .1 has been seen by Simroth or Fritz Muller, but in other respects the larva r 2 resembles the stages in the development of Megathyris p and Terebratulina which immediately precede fixation.
Norman, Terebratulina caput-serpentis L., Terebratula (Gwynia) capsules Jeff., Magellania (Macandrevia) cranium Mull.,M.
Below 150 fathoms they are rare, but a few such as Terebratulina wyvillei are found down to 2000 fathoms. Lingula is essentially a very shallow water form.