Visce7'a of Brachiopod. 233 



in the adult condition of the pedunculate, thoug-h, as it is 

 always the free valve, it occupies the reverse position in the 

 adnate Brachiopoda. 



X. Heart, unilocular as in all Brachiopoda, and globular as in 

 the articulate division of the class. Its position justifies the 

 application of the term ' dorsal ' to the valve in relation 

 with it. 



0. Mouth, immediately posteriorly to which the main nerve 

 g-ang-lia, three in number, one placed mesially and two 

 laterally, were sitiiated, forming- the under side of an oeso- 

 phag-eal collar, completed by commissural cords passing- up 

 to join on either side a gang-lion of small size at the base of 

 either arm. 



Oe. Oesophagus ; of considerable length, the mouth being so near 

 the ventral valve. 



h. Liver, surrounding the stomach, into the cardiac end of which 

 it opens by four ducts. Immediately below the posterior 

 lobe of the liver the intestine is seen passing downwards, 

 and slightly tapering in its course towards the ventral valve. 

 Having reached the valve it tiirns a little upwards and back- 

 wards, to end at a in a coecal extremity, as in other articulate 

 Brachiopoda. 



a. Coecal extremity of digestive tube The simple curve de- 

 scribed by the digestive tube of the Rhynchonella has its 

 concavity directed towards the ventral valve, just as the 

 primary curve of the digestive tract of the inarticulate 

 Ling'vda, which differs however from it by not ending 

 coecally, and by having convolutions superadded to it, of 

 which the intestine in the articulate species is desti- 

 tute. 



T. Tentacular cirrhi upon portion of left arm. The mouth, as in 

 all Brachiopoda, is situated between the points of junction 

 of the two arms to the visceral mass. 



T. Sac, or ampulla, in connection with the great brachial canal ; 

 serving prol)ably to increase the surface tlirough which the 

 fluids in the perivisceral cavity and in the brachial canals 

 can act upon each other. 



1/ . Crural lamina, arising- from hinge process of upper valve in 

 Rhynchonella for the support of the right arm, which has 



