HOLOTHURIOIDEA 415 



2. Mouth opening^ surrounded by 5 or 10 larger, valve-like plates 3 

 Mouth opening surrounded by a variable number of smaller, 



usually not valve-like plates ..... 6 



3. Mouth opening surrounded by 10 valve-like plates, regularly 



alternating large and small. (Koehler, Echinod. " Caudan ", 



p. 119, PL XXVII. 12-14) . . . Ps. tesselatus Koehler 



Mouth opening surrounded by 5 (rarely more) ^ large, valve - 



like plates ......... 4 



4. Inside the point of the valves some small plates are found 



2. Ps. squamatus, young 

 No small plates inside the point of the valves ... 5 



5. Scales smooth, about 5 between oral and anal opening ; deposits 



of sole scarce, only flat plates with small knobs ; no cups 



3. Ps. valvatus Ostergr. 



Scales granulated, about 10 between oral and anal opening. 



Deposits of sole numerous, both plates and cups (Theel, 



" Blake " Holoth., p. 12, Fig. 6) . Ps. operculatus Pourt. 



6. Deposits of ventral sole cups and larger, complicated bodies 



(Fig. 252) . . . . .1. Ps. phantapus, young 



Deposits of ventral sole only small, flat plates (Fig. 254) . 7 



7. On the dorsal side, between oral and anal opening, small scales 



intermingled with the large ones. Very small form (" Talis- 

 man'" Holoth., p. 512) . . . . Ps. nummularis Perr. 

 Large scales between mouth and anus not intermingled with 

 small ones ......... 8 



8. Shape broad, oval; scales very large, 8-10 in a series between 



mouth and ana] opening . . 2. Ps. squamatus Koren 



Shape elongate, narrow ; scales smaller, ca. 20-25 in a series 



between mouth and anal opening (Theel, " i?ZoA:e " Holoth., 



p. 14, Fig. 6) . . . . . Ps. Pourtalesii Theel 



1. Psolus phantapus (Strussenfelt) . (Fig. 251.) 



Body rather high and vaulted ; anterior and posterior end 

 promment, especially the posterior end produced into a long, 

 conical, tail-like prolongation. Body wall thick, scales rather 

 small, granulated, in large specimens hardly discernible without 

 special preparation. Ventral sole rather small, rectangular, 

 narrower than the body. Tube-feet in the mid-radius in a 

 complete series in the whole length of the sole. The two 

 dorsal retractor muscles attached to the body w^all in the 



1 For the sake of simplicity the term "mouth opening" is used here; in 

 reality it is not the mouth opening but the opening through which the 

 tentacles and — in larger specimens — the whole fore-end (the " introvert ") 

 are evaginated. 



2 Some of the valves may be subdivided into two halves. 



