20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



the entire inner chamber of the brachiopod shell probably was smooth, 

 but the areas where muscles attached seem to weather or silicify in a 

 manner that produces a smoother ultimate surface. 



The spatulate outline of the camarophorium is similar to that of the 

 muscle area in many brachiopods. Apparently the anterior adductor 

 muscles attached in a narrow band along each side of the midline, be- 

 ginning just anterior to the intercamarophorial plate, and extending 

 anteriorly onto the small, toothlike median extension of the spoon of 

 the camarophorium. The posterior adductors attached lateral and 

 posterior to the smaller pair of muscles, apparently utilizing the ante- 

 rior part of the intercamarophorial plate for additional surface. Lateral 

 boundaries of the posterior adductor muscle marks have not been ob- 

 served ; probably the muscles attached over the remainder of the con- 

 cave surface of the camarophorium. 



Davidson (1853, p. 96) suggested that the adductor muscles at- 

 tached near the base of the septum of the camarophorium. If they at- 

 tached there, the spoon of the camarophorium would have acted as a 

 "spreader" for the muscles, and they could have attached in the deep 

 transverse groove on each side of pedicle valve floor. Several objec- 

 tions to this possible arrangement are apparent. The surfaces of the 

 transverse grooves do not resemble those of muscle areas in other 

 groups of brachiopods; they do not appear to be muscle marks or 

 tracks. Instead they are like the remainder of the valve floor and prob- 

 ably represent pallial grooves or gonocoels. Moreover, no muscle marks 

 are apparent on the septum or the convex surface of the camarophor- 

 ium. 



Further objection to Davidson's proposed muscle arrangement is in 

 its radical departure from that of all other groups of brachiopods. The 

 adductors in this pattern must necessarily attach lateral to the diductors 

 in the pedicle valve, because the spondylium would have confined the 

 diductors too narrowly for them to have occupied the entire width of 

 the transverse grooves in the floor. The same would be true if they 

 attached to the outer surface of the spondylium (where no muscle 

 marks have been observed) rather than within it. The normal arrange- 

 ment in all other groups that have these sets of muscles is for the ad- 

 ductors to be doubly paired in the brachial valve, but single-paired and 

 median in the pedicle valve. Furthermore, no division into anterior and 

 posterior adductors seems possible with the proposed arrangement. 

 These departures from the normal pattern for muscles in brachiopods 

 seem too extreme to accept without convincing evidence. 



If the adductor muscles attached within the camarophorium, they 

 also must have attached within the spondylium of the pedicle valve. 



