364 



ECHINODERMS OF THE BRITISH ISLES 



ventral side. Colour in life rosy or light violet, the ventral side 

 somewhat darker. Grows to a length of ca. 22 cm. 



The varieties cylindrica and 4-lineata of Perrier are only 

 founded in various stages of contraction due to preservation 

 and thus cannot be upheld. 



Fig. 216. 



-Wheels of Benthogone rosea, from above and in side view, x 200. 

 (After Perrier, " Talisman " Holoth.) 



In British seas this species has been found in considerable 

 numbers off the S W. coast of Ireland, in depths of ca. 1200- 

 1765 m. (" Helga "), It is elsewhere known from the Bay of 

 Biscay, the Azores, and off the African coast, down to the Cape 

 Verdes. Bathymetrical distribution ca. 1000-2320 m.^ 



[Family Elpidiid^] 



Body usually short, oval, sometimes almost globular. Ten- 

 tacles usually 10 (thus in all the Atlantic forms). Dorsal papillae 

 few, not equally distributed along the radii, their calcareous 

 deposits not longitudinally directed. Few, but fairly large tube- 

 feet in the latero- ventral ambulacra, the mid-ventral ambulacrum 

 naked. Calcareous deposits pointed rods or cruciform bodies ; 

 more rarely wheels occur, but always scarce in numbers. Cal- 

 careous ring composed only of the five radials, which are star- 

 shaped, not coalesced. Statocysts are present. Gonads one or 

 more bundles of small caecal sacs. Mesentery consisting only of 

 isolated threads, entirely lacking along the second intestinal loop ; 

 a caecum may be present on the rectum. ^ 



^ The statement of its occurrence at a depth of only 16 m. (Cape Verde, 

 Princesse Alice ") evidently rests on erroneous labelling. 



^ This caecum, which occurs only in the subfamily Elpidiinse, has 

 generally been regarded as a rudimentary respiratory tree. According to 

 the recent researches of Ekman it would appear, however, that such inter- 

 pretation is erroneous. The cloaca of Elpidiids evidently has no respiratory 

 function, neither can the caecum therefore have such a function. Also the 

 ventral position of this caecum is against the homology with the mostly 

 dorsally placed respiratory trees of other Holothurians. 



