NO. 3 BURGESS SHALE FOSSILS WALCOTT 2^ 



Dimensions. — The largest specimen has a length of 17 mm., but 

 the average length is from 5 to 8 mm. 



Appendages. — One specimen has several thoracic endopodites out 

 of place on one side, and other specimens show the proximal joint 

 obscurely but sufficiently well to recognize them ; another specimen 

 has what may have been slender antennae projecting from beneath 

 the flattened labrum and posterior to it three pairs of slender ap- 

 pendages in which all traces of joints have disappeared ; there are also 

 on this specimen several threadlike, silvery lines extending from the 

 central axis out to a margin w^iich indicates that the limbs were long 

 and slender ; none of the specimens clearly show the exopodites or any 

 details of the limbs. Specimens of MarrcUa and Burgessia often 

 have threadlike, silvery lines representing the limbs, these lines being 

 the pyritizcd contents of the joints, the test having disappeared in the 

 process of mineralization of the original specimen. 



Digestive organs. — -The stomach is represented by an enlargement 

 of the anterior portion of the intestine within the cephalic carapace, 

 and the intestine extends back to the last segment ; traces of hepatic 

 caeca also occur beneath the cephalic carapace adjacent to the stomach. 



Observations.- — This very delicate form was placed, when sorting 

 the collections, among specimens of the young of Marrella splendens, 

 but it became evident upon close examination that they were quite 

 distinct. They have a dorsal shield resembling that of Naraoia. I 

 have examined all the specimens in hopes of finding free segments, 

 but without results. There is no well-defined border about the pos- 

 terior dorsal shield as in Naraoia, but there is a definite margin that 

 is unbroken by the extension of the fused segments beyond it. 



The almost complete flattening of all the specimens prevents any 

 comparison with the median lobe of the trilobites. and there is no 

 indication of facial sutures although there arc slight traces of eyes 

 on the cephalic shield at about the same place as in Natliorstia.^ 



Holotype.—U. S. N. M., No. 83950. 



MOLLISONIA Walcott 1912 



MOLLISONIA ? RARA Walcott 



Plate 21, fig. 4 



Mulli.sonia ? rara Walcott, 1912, Smithsonian Alisc. Coll., vol. 57, no. 6, p. iy8, 

 pi. 24, figs. 6, 7. 



Original description. — " Of this species there are several fragmen- 

 tary specimens. The species dififers from M. gracilis, with which it is 



^Smithsonian Misc. Coll., vol. 57, no. 6, pi. 28, fig. 2, 1912. 



