204 U.S. NATIONAL MUSEUM BULLETIN 2 58 



Pleusirus, new genus 



Diagnosis. — Mandibular molar obsolete, lacking grinding surface; 

 maxillipedal palp article 3 not produced; antennae long, peduncle 

 of antenna 1 very short; gnathopods well developed, eusirid in struc- 

 ture, fifth articles long and bearing broad posterior lobes of medium 

 depth, sixth articles attached to the produced apices of fifth articles. 

 Generic name masculine, combining characters of pleustids and 

 eusirids. 



Type species.- — Pleusirus secorrus, new species. 



Relationship^ — The eusirid-like gnathopods of this species are 

 distinctive among the Pleustidae, thus warranting erection of a new 

 genus. In antennae, mandibles and maxillipeds the genus approxi- 

 mates Parapleustes Buchholz. Pleusirus is not assignable to the 

 Calliopiidae because of the characteristic pleustid lower lip. In the 

 Calliopiidae the genus Sancho Stebbing has a second gnathopod 

 which is sub-eusirid in structure but the first gnathopod is not. 



Pleusirus secorrus, new species 



Figures 56, 57 



Diagnosis. — With the characters of the genus. 



Description.- — Only 4 specimens are available, all having antennae 

 or pereopods largely broken, with only one set of antennae being 

 available; antennae long, peduncle of antenna 1 very short and stout 

 for the family; rostrum of medium size, about as in Parapleustes 

 and Neopleustes; eyes subcircular to oval; upper lip slightly and 

 asymmetrically incised; mandibular molar evident only as slight 

 bulbous ridge running proximally from spine row; left mandible with 

 enormous, flabellate lacinia mobilis (it has been examined carefully 

 and is not a structure of the next instar), lacinia mobilis of right 

 mandible, if present, not distinct from spines of spine-row; outer 

 plate of maxilla 1 with 9 spines of characteristic placement and 

 morphology (see figure), palp 2-articulate; inner plate of maxilliped 

 with medially located, subterminal spine on outer face, apex with 2 

 blunt medial spines, one middle seta and one sharp lateral spine, 

 outer plate poorly spinose; pereopodal dactyls smooth except for 

 one small, deeply immersed subterminal seta; second articles of 

 pereopods 3-5 smooth posteriorly; body lacking dorsal processes; 

 other parts typical of pleustids shown in figures. 



Holotype.- — AHF No. 622, ovigerous female, 3.5 mm. 



Type locality. — Station 43-B-2, Cayucos, California, January 5-6, 

 1962, on four cobbles buried under boulders. 



Material. — cayucos: buried cobbles, rare, goleta: Macrocystis 

 holdfast, 3 m., rare, la jolla, one specimen collected by Dr. R. J. 

 Menzies, June 14, 1947. catalina island: "Velero" station 1871, 

 25 fm. 



