408 ECHINODERMS OF THE BRITISH ISLES 



material. Development unknown ; the breeding season appears 

 to be in winter. 



In British seas this species appears to occur all round the 

 coasts from Plymouth to the Shetland Islands, and on the east 

 coast down to Northumberland. It is elsewhere distributed 

 from the Trondhjem Fjord to the Mediterranean. Bathy metrical 

 distribution ca. 10-1050 m. 



3. Thy one inermis Heller. (Fig. 246.) 



(Syn. Thy one aurantiaca Costa ; Th. elegans Norman.) 



Body fusiform, attenuated towards the ends, but the posterior 

 end not drawn out into a long, tail-like prolongation. Body wall 

 thin, very delicate, transparent, devoid of calcareous deposits, 

 except in the posterior end, where small, more or less regular 

 disks, with a spire composed of 2 rods, are found. Tube-feet 



'iVtfW^iTr'r^ I '•"'''' ' ' "y * .' • i*i.ii'ii» > I * iM w»Mi-4rYi \j M 'i,,r,'ii';;'. '■ II- - " 



Fig. 246. — Thy one inermis. Slightly reduced. (After Herouard, 

 Recherches s. I. Holoth. cote de France.) 



without spicules, only the terminal disk w^ell developed. Tentacles 

 " completely clothed in a scaly investiture of irregular-shaped 

 cribriform calcareous plates." ^ Colour in life rosy. Grows to a 

 length of 15 cm. 



Biology and development unknown. 



In British seas this species has only been found at the Shet- 

 land Islands (Norman) ; but it cannot be doubted that it will 

 prove to occur also at least along the west coasts. It is 

 elsewhere known from the Bay of Biscay, the Azores, and the 

 Mediterranean. Bathymetrical distribution ca. 30-180 m. 



II. Subfamily Phyllophorin^ 



Tentacles 15-30, larger and smaller, so arranged that a pair 

 of larger tentacles are found in each interradius, one or more 



^ Thus stated by Norman in his description of Thyone elegans, while 

 nothing is said about it in other descriptions of Th. inermis. The author 

 has not himself had the opportunity of examining this species. 



