DAVIDSON — PAL^ONTOLOGICAL NOTES ON THE BRACHIOPODA. 107 



very apparent in Producta and Aulosteges, but are not observable 

 either in Sfrophalosia or Chonetes. 



The internal surface of the valves in all the family is covered with 

 innumerable granulations, some of which are thought by Mr. Hancock 

 to have been "probably produced by the muscular bands which 

 retracted the margin of the mantle." 



We will now describe the internal appearances observable on the 

 concave surface of the larger or ventral valve. A narrow mesial 

 ridge, originating under the extremity of the beak, separates the two 

 large elongated, ramified, or dendritic impressions which have been 

 referred by Mr. Woodward and myself to the adductor or occlusor 

 muscles ; and in this opinion we have Mr. Hancock's concurrence, for 

 it is the position occupied by the same muscle in all the articulated 

 genera of Brachiopoda with which we are at present acquainted. 

 This view is, however, dissented from by the distinguished Russian 

 palaeontologist and geologist, Count Alex. Von Keyserling, as well 

 as by some others who consider these impressions attributable to 

 ovarian sinuses, and who would go the length of supposing that 

 Froducta did not require adductor or occlusor muscles ; but the 

 largely developed cardinal process seems to denote that there must 

 have been divaricator or cardinal muscles, and in all probability 

 powerful ones ; then, why should we not conclude that Froducta, like 

 their congeners, had also occlusor muscles. Count Keyserling doubts, 

 likewise, the possibility of muscular fibres even producing dendritic 

 impressions, but in the Fectinidce {e.g. Spondylus), as well as in the 

 Unionidce, dendritic and granular muscular scars are not uncommon ; 

 and I am informed by Mr. Hancock that in Anomia patelliformis 

 there is one with radiating lines. Professor King refers the large 

 scars above described to cardinal or divaricator muscles, so that there 

 exists a difference of opinion relative to the origin of the large 

 dendritic impressions in Froducta, which occupy a considerable portion 

 of the umbonal cavity. 



In Chonetes these impressions are similar in position, but of smaller 

 proportions. 



In advance of the large scars we sometimes (in Froducta) perceive 

 smaller impressions closely connected with the larger ones above- 

 described (PI. III. and IV. c). Professor King — and I believe correctly 



