4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 122 



Key to Species of Genus Lissothuria 



1. Dorsal scale covering incomplete nutriens (Clark) 



Dorsal scale covering complete 2 



2. Rosettes present in tentacles 3 



Rosettes absent from tentacles 5 



3. Sole deposits include cups ; plates in sole knobbed . . antillensis, new species 

 Sole deposits plates only; plates smooth or with inconspicuous knobs . . 4 



4. Hourglass-shaped deposits closely resemble cups; average height of towers 



0.1 mm. Caribbean braziliensis (Theel) 



Hourglass-shaped deposits of "typical" form; average height of towers 0.27 

 mm. Eastern Pacific ornata Verrill 



5. Deposits in sole include strongly knobbed plates that tend to become 2-layered 



deichmannae, new species 

 No such plates in sole 6 



6. Sole deposits include cups; hourglass deposits absent. 



mortenseni, new species 

 Cups absent from sole; hourglass deposits present 7 



7. Towers absent; 7-8 scales between oral and anal apertures. 



veleronis (Deichmann) 

 Towers present; ca. 14 scales between oral and anal apertures. 



hancocki (Deichmann) 



Distribution. — The eight known species in the genus resemble 

 each other in so many respects that it seems likely that the genus is a 

 relatively young one, arising (perhaps from some Psolidiiim-like 

 ancestor) in the Caribbean or Eastern Pacific and dispersing across 

 the Isthmus of Panama when it was below sea level, perhaps during 

 the early Tertiary. At the present time, six species are known from 

 the Eastern Pacific and two from the Caribbean region. This 

 suggests that the migration was from west to east. The distribution 

 of this genus is paralleled by other genera in the Holothuroidea, and 

 it is known that at least 10 species of holothurians are common to the 

 Pacific and Atlantic sides of the Isthmus of Panama. 



Lissothuria ornata Verrill 



Figures 1, 2f-l 



Lissothuria ornata Verrill, 1867, p. 322. 



Psolus ornatus.— Theel, 1886a, p. 127.— Ludwig, 1892, p. 350. 

 Thyonepsolus beebei Deichmann, 1937, p. 172, fig. 3; 1938, p. 382; 1941, p. 139, 

 pi. 28 (figs. 1-3). 



Diagnosis. — Dorsal scale covering complete. Deposits of dorsal 

 surface are perforated plates, towers, and hourglass-shaped deposits; 

 no cups. Deposits of sole are perforated plates, which are smooth or 

 with a few rounded knobs. Tentacles with rosettes. 



Description of holotype.^ — ^Specimen cut transversely at middle 

 of body. Total length 51 mm, greatest breadth 18 mm, height at 

 center 10 mm. Mouth anterodorsal, anal aperture posterodorsal. 

 Oral aperture surrounded by numerous irregular valves wdth 



