22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



Rostral plate. — A small triangular rostral plate with narrow, sharp, 

 longitudinal median ridge has been seen in four specimens (see fig. 3, 

 pi. 19; fig. 2, pi. 20) ; it is located in the median line between the 

 antennae. 



Dimensions. — The average length of an entire adult specimen is 

 from 40 to 50 mm., the carapace being about 16 mm. in length with 

 a width when flattened of 15 mm. The general proportions of the 

 various parts are shown by figure 4, plate 27, of the 191 2 paper. 



Eyes. — The eyes are relatively large and placed at the end of a 

 stalk or peduncle that projects from beneath and on each side of the 

 rostral plate as seen from above. The peduncles are slender at their 

 proximal end and expanded in a broad oval outline on the distal third 

 of their length, the expanded section carrying the elongate oval visual 

 surface ; the peduncle appears to have had at least one joint at about 

 the inner third of its length and to have been attached to a prostomium 

 at its proximal end. 



Cephalic appendages. — These consist of a pair of long jointed 

 antennae that project forward beside and beneath the median rostral 

 plate, and a pair of short lobelike antennules appear to be represented 

 close to the eye and above the antennae (see fig. 3, pi. 19 ; fig. 2, pi. 20) 

 in several specimens. Traces of three pairs of cephalic limbs have 

 been observed but their structure and form are unknown. 



Thoracic limbs. — A number of specimens have five strong thoracic 

 limbs that extend from their union with the body trunk forward and 

 outward beyond the edge of the carapace (see fig. 2, pi. 18) ; the distal 

 joint is short and has three strong and two small curved spines project- 

 ing from its outer end and fine spines along its margin ; the three next 

 joints are rather short and spiniferous, but the detailed character of 

 the remaining joints is unknown. The limb observed is assumed to be 

 the endopodite of a biramous limb, but the exopodite was not de- 

 veloped or it was so small and delicate as not to be preserved in the 

 fossil state. 



Abdonii)ial limbs. — Each of the abdominal limbs is represented by 

 long, multi- jointed exopodites bearing long, slender filaments (see 

 fig. 3, pi. 20). The proximal joint was probably short and without 

 fringing filaments, but none of the specimens proves this to have been 

 the case ; the exopodites are rather large at the proximal end, tapering 

 gradually to a slender, flexible terminal section ; the filaments of the 

 terminal section are sometimes gathered in tufts or bundles as shown 

 by figure 3, plate 20. The filaments are usually flattened and matted 

 together, but a few specimens show them to have been slender, 

 cylindrical tubes similar to the filaments on the exopodite of Marrella 



