444 Deep-sea Trawling off the 8.W. Coast of Ireland : 



is distinguished from the commoner form he enumerates the 

 spines, !S. piirp\ireus\\^\m^ " radiolis primariis eminentiori- 

 bus colore albicante insignibus ; " but the differences between 

 the two species in this particularare nuicli reduced when a series 

 is examined. On the other hand, wliether specific characters 

 are useful or not, spines are certainly valuable to the indi- 

 vidual which possesses them. As the accompanying measure- 

 ments show, the form of S. Raschi may vary a good deal, and 

 these variations must affect such characters as are indicated 

 by such expressions as " ambitu fere orbiculato, dorso multo 

 minus convexo, margine magis rotundato." This brings us 

 to anotlier still unsettled question : — How far are characters 

 that vary within considerable limits to be used as specific 

 characters ? and to such a question we can well imagine 

 different systematists giving very different answers. 



Questions like these may well be raised, if the answers 

 that are given are tentative and not dogmatic. The only 

 moral I can definitely see is one which has been, but must 

 again and again be, insisted on. The definitions of species are 

 often drawn up from a few specimens, or perhaps only one ; 

 with increased knowledge of the representatives of such species 

 our judgment as to its characters is bound to be affected by 

 the variations which will undoubtedly present themselves — 

 very much so when tlie describer has a small knowledge of 

 the group — to some extent even when the description is by 

 the hand of a master in his science. 



Among the specimens is one which is considerably depressed 

 and deformed ; but the abnormal characters which it presents 

 do not seem to throw any light on the characters of the species. 



Measurements o/'Spatangus Raschi. 

 Percenta2:e value of 



Brissopsis lyrifera^ Forbes. 



Two spineless specimens, of ordinary size, were taken in 

 5 fath. 



V. H L O T H U R I I D E A. 



Holothuria tremula, Gunner. 



Dredged at 100 and 315 fath. ; it was dredged from greater 

 depths than these by the Norwegian North-Sea Expedition. 



