500 Arthur E. Shipley 



portion wliere there is a narrow deep indentation dividing the lopho- 

 phore nearly into two equal halves; this is caused by the triangulär 

 septiim mentioned above. These halves correspond with the two arms 

 of other Brachiopods. The lophophore is attached anteriorly and anterio- 

 laterally to the mantle lining the shell , postero-laterally it is attached 

 to the free edge of the triangulär plates ; in the median posterior portion, 

 it is continuous with the remaining body wall. In the median line it 

 is attached on each side to the free edge of the septum. The lophophore 

 carries round its margin a number of tentacles ; the number increases 

 with the age, but is usually from 70 to 100. Within the bases of the 

 tentacles, a lip runs entirely round the lophophore , formiug a groove 

 (figs. 2 and 15) ; the mouth lies in the posterior median portion of this 

 groove. The remainder of the lophophore is composed of a membrane 

 which Covers some of the viscera ; the centre of each half of this mem- 

 brane is rather thickened and presents in the fresh state an ili defined 

 whitish patch. The tentacles usually lie pointing towards the centre of 

 each half, but they are often curved and sometimes coiled like a cork- 

 screw. I bave never seen the tentacles protruded through the open shell 

 in the naturai state, but when the'animal is killed by immersion in weak 

 acetic acid, it always protrudesHts tentacles. On the lophophore of 

 one Argiope, I found a semi-parasitic Copepod which Dr. Giesbrecht 

 informs me, belongs to an entirely new genus which has affinities with 

 the Lichomolgidae. 



The shape of the body cavity is very complicated; at the posterior 

 end it is nearl}^ square , more anteriorly invaginations at the side take 

 place to form the brood pouches, these gradually become deeper, and the 

 posterior part of the lophophore appears in the dorsal wall of the pouch 

 (fig. 7) . Finally the pouches meet in the median line and then we bave 

 two portions of the body cavity, one lying in the ventral shell, which is 

 soon obliterated by the fusion of its walls ; the other lying in the dorsal 

 shell. This is enclosed on one side by the lining of the shell, on the other 

 by the lophophore ; it soon becomes divided into two lateral halves by 

 the appearance of the triangulär septum (fig. 3). 



Around the edge of the lophophore between the base of the ten- 

 tacles and the origin of the lip, there runs a canal in the substance of the 

 lophophore (figs. 2 and 15 ca). This is larger at its outer end but dis- 

 appears in the centre by the fusion of the inner wall to the outer. In 

 the posterior median line this inner wall passes in on each side to form 

 one of the mesenteries supporting the alimentary canal. Thus the cavity 

 in the lophophore communicates with part of the body cavity. From 



