AET. 27 NEW MIDDLE CAMBRIAN FOSSILS ^RUEDEMANN 5 



proceed from the anterolateral corners of the head. Both are funda- 

 mentally biramous, dividing into two principal branches, which in 

 turn send out a series of secondary, filamentous branches bearing 

 setae on one side. The first pair, which is the shorter, is directed 

 forward, the second sideways. Only one of the first pair (on the 

 right side) of sw^imming appendages is preserved. The protopodite 

 is short and stocky. One of the branches (exapodite) has only the 

 base preserved; the other branch (endopodite) bears four or five 

 (one displaced) long, flexuous, secondary branches and shows the 

 base of a fifth or sixth. The series of secondary branches on the 

 exopodite from the four bases shown on the stump in front of the 

 head, as drawn in the restoration (pi. 5), are conjectural. We can 

 not determine whether this first pair of appendages represents the 

 first pair of antennae or the second; if the latter, the first pair of 

 antennae may have been small or very tenuous. 



The second pair of swimming appendages is by far the larger 

 of the two and may either represent the second pair of antennae or 

 may correspond to the mandibular foot of the nauplius. (See under 

 Eelationships.) The protopodite is again short and powerful and 

 appears to consist of two joints. The forward division of the foot, 

 which we take to be the exo]oodite, is extended horizontally and 

 reaches a length of 20 mm. ; the number of its joints can not be defi- 

 nitely established. On one side it bears 7 to 11 thin flexuous sub- 

 branches (exites) and on the other about 6, which branch off nearer 

 the base. The posterior division of the swimming foot, according to 

 our view the endopodite, curves backward nearly parallel to the 

 body, giving off about 10 slender, thin endites, about 14 mm. long, 

 on the outer side of the branch, and terminates in a similar but 

 shorter (9.5 mm.) endite. 



All the exites and endites are provided with short setae on one 

 side. These, however, may be only the bases of longer bristles, since 

 there is one fragment that retains long stiff setae on the portion of 

 the swimming appendage preserved. 



On the left side are three simple legs, tAvo of which undoubtedly 

 proceed from the underside of the head, and the third (not drawn on 

 restoration) appears to do so. On the right side are the bases 

 of what appear to have been abdominal feet, the stumpy second, 

 however, being doubtful. There is no evidence of a biramous struc- 

 ture or of gills, the exopodites apparently alone protruding beyond 

 the body. 



Occurrence. — Middle Cambrian, Stephen formation (Loc. lis), 

 Mount Stephen, British Columbia. 



Holotype and paratypes. — U.S.N.M. No. 83485. 



Relationships of Marria. — There is no fossil crustacean that can be 

 directly compared with Marria walcottL The only fossil form that 



