AKT. 27 



NEW MIDDLE CAMBEIAN FOSSILS EUEDEMANK 



13 



(5) The " labrum " {Ih in pi. 26, fig. 2) is a typical trilobite hypos- 

 toma, similar to that of Neolcnus serratus and Ogygo'psis klotzL 



(6) The muscle attachments, shown as rows of tubercles on the 

 axial lobe of the abdomen (in pi. 25, figs. 1 and 5; pi. 26, figs. 3 and 

 4) are exactly the same as repeatedly figured for trilobites, for ex- 

 ample, by Hall and Clarke ^ from specimens where the test was either 

 exfoliated or transparent. 



(7) According to our material and Walcott's drawings, the legs, 

 both of the carapace and abdomen, are the same as those of trilobites. 

 The gills of the third to fifth legs of the head are, for instance, well 



FiGCRB 5. — A young trilobite with large cephalon, showing in 

 white the portion preserved in the specimen of Marrella 

 splendens: a. Frontal tissue strand of cephalon ; ij posterior 

 tissue strand of cephalon and genal spines ; c, axial lobe 

 of thorax ; d, proximal portion of pleura 



shown in Plate 25, Figure 3 — on the right side — also in Plate 26, Fig- 

 ures 3 and 4. All legs possess " the jointed leg-like endopodite, a 

 jointed setiferous exopodite, and expanded gill-like epicoxite," which 

 Walcott recognized only for those of the abdomen. 



(8) The abdomen in the molted specimens retains only the axial 

 lobes without the pleura, a feature that has aided strongly in obscur- 

 ing the trilobite nature of Marrella. It is probable that, as in the 

 case of the cephalon, the pleura were represented by thin soft mem- 

 branes, which later in life gave rise to the harder chitinous shell. 

 (Fig. 5.) Possible traces of thicker tissue strands in these pleural 



» Paleontology of New York, vol. 7. pi. 23, fig. 8 ; pi. 25, flg. 8 ; 1888. 



