NO. 6 MIDDLE CAMBRIAN BRANCHIOPODA, ETC. 193 



MARRELLA SPLENDENS, new species 



Plate 25, figs. 1-6, and plate 26, figs. 1-6 



The general form is shown by figures i, 4, and 5, plate 26. The 

 exoskeleton is composed of a strong cephalic carapace (c) (fig. i, pi. 

 26) which extends as two long, strong, curved spines (x) that con- 

 tinue posteriorly over the back of the thorax beyond the end of the 

 body. At each antero-lateral angle a strong, backward-curving spine 

 (a') complements the great dorsal thoracic spines. A pair of large 

 crescentiform sessile eyes occur on the anterior margin just within 

 the base of the anterior spines (pi. 25, figs. 4 and 5). The great 

 dorsal spines are beautifully crenulated on the outer margin by short, 

 strong backward-curving spines. 



Appendages. — The antennae (a", fig. 5, pi. 26) are long, slender, 

 and many- jointed ; they unite with the head near the posterior end of 

 the labrum ; the third pair of appendages, mandibles (m), are large, 

 long, 7 ?-jointed and with fine setae on the edge of the joints which 

 give the appearance of a slender feather to the appendage (fig. 3, pi. 

 25, and fig. 3, pi. 26). The fourth and fifth cephalic appendages are 

 slender, and with long joints. 



There are 24 pairs of thoracic appendages. Each one is composed 

 of a jointed leg of seven joints with a flattened, short, broad spine on 

 all but the proximal and distal joints (thl, fig. 6, pi. 26) ; ten legs, 

 (endopodites) with the expanded joints are shown in figure 6, 

 plate 26 ; anterior to these there are preserved 4 setiferous 

 appendages that appear to be the exopodites of the leg. These are 

 more fully shown by figure 6, plate 25, also figure 3. Another view 

 of the long, jointed endopodite is found in figures 3 and 5, plate 26. 

 The presence of a gill (epipodite) was unsuspected until the specimen 

 represented by figure 4, plate 26, was found ; this fine example is so 

 delicate and so beautifully preserved that it is almost unique even 

 among the wonderful Burgess shale fossils. 



Abdomen. — The abdomen (ab, figs, i, 3, 4, and 6, pi. 26) forms a 

 small, plate-like termination of the long body. 



Interior structure. — The alimentary canal is very distinct in a 

 number of specimens (i, figs. 3 and 6, pi. 26). It extends from the 

 posterior margin of the labrum back to the plate-like abdomen. The 

 head is too much smashed down to show any details of interior struc- 

 ture, but the alimentary canal appears to widen out and occupy much 

 of the space beneath the subquadrangular carapace. The large dorsal 

 spines have a central canal that appears to open into the space 

 (stomach ?) beneath the carapace; this canal may represent the 

 4 



