NO. 3 BURGESS SHALE FOSSILS WALCOTT I3 



pendages are posterior to the hepato-pancreatic tubes passing from 

 the stomach to the hepatic caeca. 



There is no clearly defined line between the cephalic and trunk 

 limbs, but from the relations of the limbs in Burgessia and Marrella 

 it is assumed that it is between the third pair of cephalic limbs and 

 the supposed first pair of trunk limbs. The specimens are too much 

 obscured by the compression they have undergone to permit of recog- 

 nition of the detailed structure of the limbs. 



Thoracic limbs. — The specimen represented by figure 3, plate 14, 

 has the distal ends of 17 thoracic or trunk limbs projecting beyond the 

 left margin of the posterior shield ; the shield in this specimen has 

 not more than 14 fused segments outlined on it, so it is probable that 

 the three anterior limbs belong with the body segments between the 

 anterior segment of the posterior shield and the third pair of cephalic 

 limbs. Another alternative is that the distal portion of the two anterior 

 limbs extending beyond the margin of the shield belong to the maxilla 

 and maxillula, which would leave only one pair of limbs from the seg- 

 ment anterior to the posterior shield and posterior to the cephalic 

 limbs. The limbs were so subject to displacement, however, that any 

 deduction is very uncertain. The distal portion of the thoracic or 

 trunk limbs shows an endopodite with a slightly curved terminal spine 

 with a slender section back of it corresponding to the slender distal 

 joint of the endopodite of Marrella and Burgessia: and then the joints 

 broaden towards the coxopodite with slight indications of five joints 

 between the distal joint and coxopodite. 



The exopodite is represented by many slender filaments that were 

 attached to a multi- jointed arm or support similar in appearance to 

 that of the exopodite of Marrella. The filaments are relatively broad, 

 as they occur flattened on the shale. There are strong indications of 

 large coxopodites, but none show their original form or the exact 

 point of attachment of endopodite or exopodite, and the joints of 

 the endopodites have been so crushed down as to be no longer definitely 

 recognizable. The exopodites were nearly as long as the endopodites, 

 and the filaments of the former are usually extended out to the end 

 of the endopodites or beyond. 



Digestive organs.- — The exact location of the moutli is unknown, 

 but from the apparent position of the antennae and proximal joints of 

 the cephalic limbs, it was posterior to the point of entrance of the 

 hepatic tubes, back of which the intestine was large with minor hepatic 

 caeca opening into it through foiu" small tubes, all of which arc anterior 

 to the posterior dorsal shield as indicated in the diagrammatic res- 

 toration (fig. 2) ; beneath the posterior dorsal shield the intestine is 



