110 GUIDE TO THE FOSSIL INVERTEBRATE ANIMALS. 
Gallery 
VIII. 
(Schizophoria) strialvla. The outer 
folds are set witli bristles (setae). All 
edges 
of the iiiantle- 
these structures are 
shown in Diagrams 5 and 11. 
Muscles pass across the body 
of the animal from one shell- 
valve to the other (Diagram 6); 
they serve to open and to 
close the valves, and to move 
them sideways. The attach- 
ment of these muscles to the 
shell forms scars, which in fos.sil 
brachiopods are the only evi- 
dence we have as to the arrange- 
ment of the muscles. The draw- 
ing from life of the inner 
surface of a Lingula .shell 
(Diagram 7 and Fig. 57) .should 
be compared with Diagram 8 showing the muscles. 
The viscera lie near the hinder or ]>eduncular end of 
the shell, with the mouth directed towards its forepart or 
Fig. 56. — Tlie internal cast of a 
Brachiopocl shell from Permian 
rocks, Camarophoria Schlot- 
heimi, showing the impressions 
of vessels in the mantle-fold. 
Fig. 57 . The muscle-scars of the Recent Lingula anatina. Interior of V, 
ventral or peduncular valve, and D, dorsal or brachial valve, n, 
umbonal ; p.s., parietal; tm, transmedian; e-l, externo-lateral ; vi-l, 
medio-lateral ; c, central ; a-l, antero-lateral. 
opening. The mouth is surrounded by a somewhat horseshoe- 
shaped°disc; this bears tentacles, furnished with minute, 
rapidly-moving processes (cilia), wdiich drive towards the 
mouth currents of water containing food-particles; it is 
