286 



ECHINODERMS OF THE BRITISH ISLES 



\Hygrosoma nranus (Wyv. Thomson).] 



(Syn. Phormosoma uranus Wyv. Thorns., Echinosoma 

 uranus (Wyv. Thorns.).) 



This species appears to be in general very like the preceding ; 

 but as it has never been duly described, it is not known whether 

 perhaps specific differences are found in 

 the arrangement of the tubercles. The 

 only character known with certainty to 

 distinguish it from H. Petersii is the shape 

 of the tridentate pedicellariae, which have 

 simply leaf-shaped valves (Fig. 162), 

 differing thus very markedly from the 

 highly involute pedicellariae of H. Petersii. 

 Colour in life unknown. Reaches appar- 

 ently as large a size as H. Petersii. 



From British seas this species has 

 been recorded from N.W. of Lewis, 

 1000 m. (" Knight Errant "), and from 

 51° r N., 11° 50' W., 1350 m. (Sladen). 

 Both these records are, however, erron- 

 eous. The former specimen is Sj^erosoma 

 Grimaldii, the latter Phormosoma 

 placenta.^ The true H. uranus is known 



Fig. 162. Valve of only from off the Portugal coast, 3145 m. 



tridentate pedicellaria (" Challenger "), and off the Saharan 

 of Hygroso?na uranus. . noo /«' rri v jh 



x33 coast, 938 m. ( Talisman ). 



4. Sperosoma Koehler. 



Test very flexible ; no sharp limit between oral and aboral 

 side, the aspect of the two sides not very different. Large 

 primary plates of the ambulacra divided into an outer, poriferous 

 and an inner, non-poriferous part (Fig. 156, 3) ; the smaller 

 primary plates of the ambulacra being rather large, the ambulacra 

 thus, in fact, are composed of 8 series of plates instead of the 

 usual 2 series. In correspondance herewith the ambulacra, 

 especially on the oral side, are very broad, as broad as or even 

 broader than the interambulacra (while in the other genera the 

 ambulacra are distinctly narrower than the interambulacra). No 



^ The two specimens in question were sent to the author for re-examina- 

 tion by the authorities of the British Museum and the Irish National 

 Museum. 



