HOLOTHURIOIDEA 397 



25° 45' W. {" Michael Sars "), 2870-3120 m. ; the latter species has 

 an almost cosmopolitan distribution, in depths of ca. 1650-4085 m. 

 Several more littoral species are found in the Mediterranean and 

 on the adjoining Atlantic coasts ; but none of these are known 

 to go so far north that there would seem to be any probability 

 of their occurring within the British area. Descriptions of these 

 species are found in Koehler's Echinodermes, Faune de France. 



Key to the species of Cucumaria known from or likely 

 to occur in the British seas. 



1. Body more or less elongate, attenuating, anterior and posterior 



end usually curving upwards ..... 2 



Body not elongate, attenuating, curving upwards . . 4 



2. Middle part of the ventral side with tube -feet especially richly 



developed, forming a ventral sole. Deposits smooth plates, 

 partlj^ imbricating {'''' Monaco ""% Ixvi., p. 117, PI. VII. 1-4) 



C. arcuata (Her.) 

 Middle part of ventral side not like a sole .... 3 



3. Body laterally compressed ; large plates of the skin imbricating, 



the free part of the jDlate covered with triangular, flat tubercles 

 (" Talisman " Holoth., p. 505, Pis. XII. 7, XXI. 20-28) 



C. compressa Perr. 

 Body not laterally compressed ; large plates of the skin not dis- 

 tinctly imbricating, qmte smooth 2. C. elongata Dlib. and Kor. 



4. Very large form ; the skin thick, leathery, almost devoid of 



spicules. (Young specimens with large, irregular plates with 



small tubercles (Fig. 239, 2).) . . 1. C.frondosa (Gunn.) 



Small forms with numerous calcareous deposits ... 5 



5. Deposits 4-armed, the ends of arms widened, thorny. Body 



fusiform ; tube-feet completely retractile, sparse, in an alter- 

 nating row along each radius (" Challenger " Holoth., ii., p. 66, 

 Pis. IV. 6, XVI. 6) . . . . C. ahyssorum Theel 



Deposits not 4-armed ....... 6 



6. Calcareous deposits smooth ...... 7 



,, ,, tuberculate ..... 8 



7. Deposits large, fenestrated plates ; no small star-shaped plates 



in the outer layer of the skin . 3. C. Hyndmani Thomps. 



Deposits small, button-like, with 4 main holes and often one 



or a few at each end ; small star-shaped bodies in the outer 



layer of the skin . . . 4. C. saxicola Br. and Rob. 



8. Small bodies in the outermost layer of the skin cup -shaped 



(Fig. 241, 2) . . . . . 5. (7. Normani Pace. 



Small bodies in the outermost layer of the skin irregular stars 



(Fig. 241, 1, 3) '.9 



9. Small forms scarcely exceeding 4 cm. length. Tube-feet scarce, 



in zigzag rows . . . . . 6. C. lactea (Forbes) 



Larger forms, up to 15 cm. in length. Tube -feet in distinct double 



series . . . . . . 7. C. Planci v. JMarenz. 



