With no hinge to the shell and with an alimentary canal open at both ends, and Testicardines (Articulata), with a hinge between the dorsal and ventral valves and with no anus, was proposed by Owen and has been adopted by nearly all authors.
The stomach then passes into an intestine, which in the Testicardines (Articulata) is short, finger-shaped and closed, and in the Ecardines (Inarticulata) is longer, turned back upon its first course, and ends in an anus.
In the Testicardines, of which the genus Terebratula may be taken as an example, five or six pairs of muscles are stated by A.
In the Testicardines, where no such sliding action of the valves was necessary or possible, no muscles for such an object were required, consequently none took rise from the lateral portions of the valves as in Lingula; but in an extinct group, the Trimerellidae, which seems to be somewhat intermediate in character between the Ecardines and Testicardines, have been found certain scars, which appear to have been produced by rudimentary lateral muscles, but it is doubtful (considering the shells are furnished with teeth, though but rudely developed) whether such muscles enabled the valves, as in Lingula, to move forward and backward upon each other.
The orders Atremata and Neotremata are frequently grouped together, as the sub-class Inarticulata or Ecardines - the Tretenterata of Davidson - and the orders Protremata and Telotremata, as the Articulata or Testicardines - i the Clistenterata of Davidson.
TESTICARDINES (ARTICULATA) ORDER III.