DAVIDSON— PALAIONTOLOQICAL NOTES ON THE BRACIIIOI'ODA. 107 
very apparent in Prochicta and Aulostec/es, but are not observable 
either in Strophalosia or Chonetes. 
The internal surface of the valves in all the family is covered with 
innumerable granulations, some of which ai-e 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 
ProdxKta 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 Producta, like 
their congeners, had also occlusor muscles. Count Keyserling doubts, 
likewise, the possibility of muscular fibres even producing dendritic 
impressions, but in the Pedinidce {e.g. Spondylus), as well as in the 
UnionidcB, 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 Producta, 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 Producta) perceive 
smaller impressions closely connected with the larger ones above- 
described (PL III, and IV. c). Professor King — and I believe correctly 
