14 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 79 



membranes may be seen in Plate 26, Figures 4 and 6, on the right 

 side, while the specimen shown on Plate 26, Figure 1, retains the thin 

 tests of the pleura themselves on both sides of the axis. 



(9) Finally, we have a specimen from our State Museum collec- 

 tion clearly showing the pygidium as a fine carbonaceous film (see 

 pi. 3, fig. 2) , a result of the retention of the thin pygidial membrane 

 after molting. 



Combining all these facts, we have no hesitation in considering 

 Marrella sylendens a trilobite in a young, freshly molted stage — 

 probably Neolejvm serratus, which possesses the same general outline, 

 especially in the carapace and pygidium. 



The caudal rami found by Walcott in Neolenus and probably 

 doubtless also present in other trilobites have not yet been seen in 

 Marrella s'plendens. They are, however, exceedingly delicate ap- 

 pendages that may well have been lost in the molting, or rather in 

 fossilization. 



From lack of material I have not taken up the supposed relation- 

 sliip of Molaria spinifera to the trilobites, suggested by Dacque. 



Half a year after the preceding discussion had been written, Dr. 

 C. E. Eesser, of the United States National Museum, informed me 

 that considerable additional material on Marrella splendens^ includ- 

 ing a number of photographs, had been found and should be used. 

 Some of these excellent pictures, which bring out additional features 

 of Marrella worth recording, are reproduced herewith. They have 

 not been retouched. 



Plate 6, Figure 1, is an enlarged portion of Walcott's Plate 26, 

 Figure 1. It shows the distinct outline of the glabella with the 

 glabellar furrows and a narrow portion of the fixed cheeks, the 

 remainder of which has been torn away along the jagged edge. The 

 flatter occipital ring is recognizable posterior to the glabella. From 

 it proceed the posterior thickened margins of the cephalon, which 

 are here turned backward. The anterior converging sections of the 

 facial suture are preserved where it crosses the frontal margin of 

 the cephalon. 



Plate 6, Figure 2, is a somewhat obliquely compressed specimen. 

 It also shows the glabella, the axial lobe of the thorax with the 

 muscular attachments of the legs, and the pygidium. The latter 

 clearly exhibits the axial lobe extending three-fourths of the length, 

 and also the marginal doublure on the left. 



Plate 6, Figure 3, again shows the cranidium with the short sectors 

 of the facial suture on the broad frontal " horns " (margins of cara- 

 pace). This specimen demonstrates the fact that with the exception 

 of the pair of antennules there are no antennae, mandibles, or max- 

 illae, which Walcott had been led to believe were present, but only 

 biramous cephalic and thoracic legs, the endopodites of which are 



