12 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 122 



Dorsal and ventral tube feet with end plates 0.21 mm in diameter, 

 and curved perforated supporting rods and plates of average greatest 

 length 0.15 mm. Tentacles with numerous rosettes (fig. 3i), larger 

 curved perforated rods (fig. 3j) and plates (fig. 3c), and smaller 

 plates (fig. 3d) . Larger perforated plates uncommon. 



HoLOTYPE. — Complete specimen, expanded, total length 10 mm, 

 greatest breadth 4.5 mm, height 4 mm. Lodged at Universitetets 

 Zoologiske Museum, Copenhagen, Denmark. 



Type-locality. — St. Thomas, Virgin Islands (date and depth 

 unknown) ; collected by A. A. Riise. 



Paratypes. — Three specimens 9x5 mm (length x greatest breadth), 

 12 X 5 mm, 9x4 mm. Locality and depository as above. 



Remarks. — While examining collections in the Zoological Museum 

 at Copenhagen, I found the above specimens labeled "Psolus antillensis 

 Liitken." I know of no reference to this species in the hterature. 

 Drs. Bent Hansen and F. Jensenius Madsen agreed that the labels 

 with the specimens were written by Dr. C. F, Liitken during the latter 

 part of the 19th century, and it appears that Psolus antillensis is one 

 of several of Liitken's manuscript names. The name is vahdated here. 



Lissothuria antillensis differs from its Caribbean congener L. 

 hraziliensis in having shallow cups among the deposits of the sole. 



Lissothuria mortenseni, new species 



Figure 4 



Diagnosis. — Dorsal scale covering complete. Deposits of dorsal 

 surface are towers and a few small plates; no cups, no hourglass- 

 shaped deposits. Deposits of sole are shallow cups and, rarely, small 

 smooth plates. Tentacles lack rosettes. 



Description. — Body approximately two-thirds as broad as long. 

 Mouth and anus dorsal, each surrounded by numerous sharply 

 pointed valves. Dorsal surface of body covered by imbricating scales 

 approximately 1.5 mm in diameter; approximately 6 scales between 

 oral and anal apertures. Scales covered by dense coat of small 

 granules. Dorsal tube feet few, minute, passing through and between 

 scales. Tentacles richly branched. 



Sole transparent, surrounded by double row of tube feet. Single 

 or triple rows not uncommon in smaller and larger specimens re- 

 spectively. Midventral radius naked or with 1 or a few tube feet 

 in larger specimens. Specimens 8-9 mm in total length aheady 

 sexually mature. Sexes separate, eggs less than 0.5 mm in diameter. 



Calcareous deposits of dorsal surface (apart from scales) are almost 

 exclusively towers of approximately same size and shape; average 

 height 0.13 mm, average diameter of base 0.13 mm (figs. 4a,b). 



