110 GUIDE TO THE FOSSIL INVEETEBRATE ANIMALS. 



Gallery 

 VIII. 



(ScMzojjJioria) striatida. The outer edges of the mantle- 

 folds are set with bristles (setse). All 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 fossil 

 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 peduncular end of 

 the shell, with the mouth directed towards its forepart or 



Fig. 56. — The internal cast of a 

 Brachiopod shell from Permian 

 rocks, Camarophoria Schlot- 

 heinii, 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, u, 

 umbonal ; p.s., parietal; tm, transmedian ; e-l, externo-lateral ; m-Z, 

 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), which drive towards the 

 mouth currents of water containing food-particles ; it is 



