465 



The author conceives that the valves are separated by the action 

 of the divaricators, combined with that of the parietals ; these 

 muscles compressing the visceral cavity posteriorly, and thus driving 

 its contents into the anterior portion. The antagonists of these are 

 the occlusors ; while the office of the adjusters appears rather to be 

 to supply the place of a hinge, and to prevent anything like sliding 

 of the valves one over the other. 



The muscular fibres of Linyula are smooth and unstriated. In 

 Waldheimia those of the posterior occlusors are strongly striated, but 

 the rest of the muscles have smooth fibres. The arms, their attach- 

 ment and minute structure are next fully described. 



In Waldheimia the canals of the attached portions of the arms 

 coalesce into a single wide tube, which lies externally between the 

 produced and reflected crura of the calcareous loop, and is separated 

 by a partition from a canal of corresponding size the "brachial 

 sinus," which also extends throughout the whole length of the pro- 

 duced and reflected crura, and is in fact a prolongation of the peri- 

 visceral chamber. The cirri are arranged in this and all the other 

 Brachiopoda examined, in a double alternating series not in a single 

 row, as has hitherto been stated to be the case. The walls of the 

 brachial canal are tolerably well supplied with delicate muscular 

 fibres, which run diagonally round the tube, and are most strongly 

 developed towards the sides, near the grooved ridge which supports 

 the cirri. An indistinct band of exceedingly delicate longitudinal 

 fibres may also be observed nearly opposite to it. The author has 

 however completely failed to discover, either here or in Rhynchonella, 

 anything like the double spiral arrangements of fibres described by 



