HOLOTHURIOIDE A 4 1 9 



Young specimens bear some resemblance to the following 

 species, having generally, like the latter, 5 triangular oral valves ; 

 but the}^ may be distinguished by the presence of some small 

 scales inside the apex of the valves, and by the anal opening 

 being surrounded by more small scales (in Ps. valvatus a single 

 circle). From young Ps. j^hantapus they are distinguished by 

 the absence in this latter species of the larger oral valves, the 

 attachment of the dorsal retractor muscles in the interradii, 

 by the deposits of the ventral sole, and by the different shape of 

 the grains on the scales. 



Development unknown. Sexual maturity is reached at a size 

 of ca. 30 mm. length. 



From British seas this species has not hitherto been recorded. 

 The author having had the opportunity of examining some of 

 the specimens recorded by Massy under the name of Psolus 

 Fabricii,^ finds that they really belong to Ps. squamatus, not 

 to Fabricii, as might well be expected, Ps. Fabricii being an 

 Arctic species, not known south of Iceland. The localities where 

 Ps. squamatus was found, in abundance, are : 51° 20' N., 11° 35' 

 W., 730-828 m., and off Eagle Island, Co. Mayo, 530-698 m. 

 (" Helga "). Most probably also the specimens recorded in 

 Bell's Catalogue from Shetland, under the name Ps. Fabricii, are 

 referable to squamatus. 



The species is known elsew here with certainty only from the 

 Norwegian coasts up to the Trondhjem Fjord. The various 

 records of its occurrence at Greenland, the coasts of N. America, 

 Japan, South Africa, etc., are uncertain and need verification. 

 Bathymetrical distribution ca. 40-400 m. 



3. Psolus valvatus Ostergren. (Fig. 255.) 



Body usually very flattened, anterior and posterior end not 

 prominent. The mouth opening surrounded by 5 large, trian- 

 gular valves which, when the opening closes, make a complete 

 cover. The valves are interradially placed, sharply limited 

 against the adjoining body scales. Sometimes one or more of the 

 valves are divided into two lateral halves. No small plates are 

 " found inside the apex of the valves. Anal opening surrounded by 

 a single circle of scales. Scales rather irregular, of various sizes, 

 not distinctly imbricating. They are quite smooth ; only in the 



^ Received from Dr. Stelfox, National Museum of Ireland, Dublin. 

 Psolus Fabricii, though resembling in general Ps. squamatus, is easily 

 distinguished by the much coarser granulation of its scales, and by the 

 presence of both cups and flat, smooth plates in the ventral sole. 



