392 ECHIN0DERM8 OF THE BRITISH ISLES 



rounded, white sj^ots on the dorsal side ; the ventral side lighter 

 eoloured. Grows to ca. 30 cm. length. 



This species is less apt to eviscerate on capture ; can even 

 live a fairly long time in aquaria. As in several other tropical 

 species, the skin Avill easily dissolve, turning into slime, in 

 specimens left some time out of the water, before preservation. 

 Development unknown. 



In British seas this species has been found off the Irish west 

 coast (" Helga ") ; the exact locality and depth unknown. It 

 is known elsewhere from the Bay of Biscay, the Canaries, and the 

 Mediterranean. Bathymetrical distribution ca. 5-400 m. 



III. Family Holothuriid^ 



Tentacle ampuUae present. Gonads only on the left side of 

 the dorsal mesentery. Respiratory trees usually connected with 

 the alimentary canal through a rete mirabile. Stone canal not 

 connected with the body wall. Cuverian organs often present. 

 Deposits usually tables and buttons or derivatives of pointed rods. 

 No C-shaped bodies. 



Mainly littoral forms, abundant in tropical seas, especially on 

 coral reefs ; many species are eaten and form an important 

 article of commerce (" trepang ", " beche de mer "). 



In British seas only the genus Holothuria is known to occur, 

 but another, Gastroihuria Perrier, is likely to occur there also, 

 the only species known, G. limhata Perr., having been found in 

 the Bay of Biscay, 564 m. (" Talisman ").i 



Key to the genera of Holothuriidce known from or likely 



to occur in the British seas. . 



Tentacle ampullae small ; respiratory trees free (" Talisman " 



Holoth., p. 469, PI. XV. 1-14) . . Gastrothuria Perr. 



Tentacle ampullae well developed ; respiratory trees connected with 



the alimentary canal by a rete mirabile . 1. Holothuria liinn. 



1. Holothuria Linnaeus. 



Mouth terminal ; usually 20 tentacles. No anal teeth. 

 Tentacle ampullae well develoj)ed ; respiratory trees connected 

 with the alimentary canal by a rete mirabile. Cuvierian organs 

 may be present. 



Only one species, Holoth. For shall D. Chiaje, known from the 

 British seas. Several more species are found in the Mediterranean 



^ According to information received from Hj. Ostergren, Gastrothuria is, 

 however, very probably only a young Stichopus regalis. 



