424 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 99 



anterior extremity, is extended laterally from each side, the lobes thus 

 produced each nearly equaling in width the central portion of the seg- 

 ment. The "width of the segment, by this lateral extension, consid- 

 erably exceeds its length. The urosome is slightly shorter than the 

 metasome. The margins of the abdominal somites are entire, ex- 

 hibiting no denticulation or spinous serration. 



The rostrum and associated structures are exceptional, unique in 

 form among members of the genus that I liave seen (fig. 37, 1) . The 

 usual beaklike spine is absent; the front of the head is produced 

 ventrally and somewhat posteriorly in a rounded lobe. The usual 

 basal chitinous plate extending posteriorly between the bases of the 

 antennules and antennae presents a remarkable modification. At a 

 level just back of the bases of the antennules, this structure is pro- 

 duced ventrally as an elongate, terminally bifurcate projection. The 

 aspect is of rather soft and flexible consistency of the thin chitinous 

 integument. The usual chitinous bars of this region are represented 

 posterior to this bilobed structure as a narrow bar, divergent pos- 

 teriorly in the shape of an inverted Y. 



The antennules are 7-segmented. The margins are rather irregular 

 in outline and show no indication of the chitinous reinforcements 

 seen in some of the species described above. The sixth and seventh 

 segments are unusually short in proportion to their width. All the 

 details of setal armature that could be made out on the two available 

 specimens are presented in the accompanying fig-ure (fig. 37, J). 



The antennae are very stocky in general aspect by comparison with 

 the other species described here. The length of the second segment 

 is considerably less than twice the greatest width. In the other spe- 

 cies seen the ratio of length to width of this segment is much greater 

 than 2. In the details of ornamentation the appendage does not 

 differ significantly from that of the other species (fig. 37, K). 



The mandibles exhibit an expansion of the basal portion of the 

 flat ciliated blade that approaches in appearance the mandible of 

 some of the species of Lichomolgus (fig. 37, L). This contour is the 

 only such instance among the members of Paranthessius that I have 

 seen, but its significance can be hardly more than a verification of the 

 rather close systematic relationship of the genera. The maxillule is 

 like that of the other species described above. The maxilla is of 

 generalized appearance, sufficiently resembling that of P. tivelae to 

 require no separate illustration. However, in P. perplexus the more 

 distal of the two setae of the terminal segment of tlie maxilla bears the 

 usual fringe of fairly heavy cilia along its distal margin as in the 

 remainder of the species treated here. 



