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was composed, it might be desirable to treat the subject under two 

 different beads in the CU si enter ata, of which the genus Terebmtiila 

 mi^ht be taken as an example, five or six pairs of muscles were 

 stated by Hancock and others to be connected with the opening 

 and closing of the valves, or with their attachment to, or movements 

 upon the peduncle. First of all, the adductors, or occlusors, consisted 

 of two muscles, which, bifurcating near the centre of the shell 

 cavity, produced a large quadruple impression on the internal sur- 

 face of the small valve, and a single divided one towards the centre 

 of the large or ventral valve. The function of this pair of muscles 

 was the closing of the valves. Dr. Gratiolet who had likewise de- 

 scribed with great minuteness, the muscles of the Brachiopoda, in- 

 formed us that those which close and open the valves were the only 

 ones known to Pallas, but that he defined their positions and 

 functions clearly. The same was done by Blainville and Quenstedt. 

 The next two pairs of muscles had been termed divaricators, or 

 cardinal muscles, and had for function the opening of the valves. 

 The divaricators proper were stated by Hancock to arise from the 

 ventral valve, one on each side, a little in advance of and close to 

 the occlusors, and after raisidly diminishing in size became attached 

 to the cardinal process, a space or prominence between the sockets 

 in the dorsal valve. The accessory divaricators were, according to 

 the same authority, a pair of small muscles which had their ends 

 attached to the ventral valve, one on each side of the median line, 

 a little behind the united basis of the occlusors, and again to the 

 extreme point of the cardinal process. Two pairs of muscles 

 appeared to be connected with the peduncle and its limited move- 

 ments had been minutely described by Hancock as having one of 

 their extremities attached to this organ. The dorsal adjustors 

 were attached to the ventral surface of the peduncle and again in- 

 serted into the hinge plate in the smaller valve. The ventral 

 adjustors were considei-ed to pass from the inner extremity of the 

 peduncle and to become attached by one pair of their extremities 

 to the ventral valve, one on each side of, and a little behind, the 

 expanded base of the divaricators. The function of these muscles 

 was not only that of erecting the shell, but also to attach the peduncle 

 to the shell, and thus effect the steadying of it upon the peduncle. 

 Such was the general arrangement of the shell muscles in the divi- 

 sion comprising the articulated Brachiopoda, allowance being made 



