464 



Variafioii ui " Ojyhioconta Nigra" 



killed by iminersion in a Solution of formaline. Then each aiiiiii.il wjis exaniined 

 aml a notc taken of 



1. The shape of the disc. 



2. The colour. 



3. The breadth of the disc. 



4. The leiigth of the longcst ray. 



5. The iiumber of rays. 



6. The Iiumber and position of the madreporic plates. 



7. Any uiiusiuil character. 



At first I confined my observations to a thousand speciniens whose dises were 

 10 mm. and ii])\vards in breadth. As the residts of this prcliininary e.vamination 

 were iutere.sting, I uext endeavoured to determinc; whether they cxtended to 

 speeimcns of all sizcs, even tlie must minute obtainable. 



Accordingly on the 27th of September the same ground near the Tan Buoy 

 was again dredged, with the result that we gatiiered over two thousand .speeimens, 

 which DU heing brought to the Station were killed by immersion in fresh water. 

 They were then preserved in a tifty per cent. Solution of alcohol for future 

 exaniination : and I shail now proceed to give the results I have arrived at from 

 my exaniination of these and the other thousand speciniens. 



1. As to shape of disc. 



One of the specific characters of this species, according to Forbes*, and Jeffrey 

 Bell-f, is that the disc is round, but au exaniination of the accompanying table 

 (Table I.) points rather to the disc beiug in general pentagoual. 



TABLE I. 



Showing the Numher of Speciniens with Circular or Pentagonal Disc. 



For convenience, let T,, T„, and T^ denote the first, second, and third thousands 

 respectively. No troubie was experienced in classifying the shapes of disc, for 

 there was scarcely a single specimen which did not readily lall into one of three 

 groups, namcly, distinctly circular as in Fig. 1, or distinetly pentagonal («) with 

 the rays at the angles of the pentagon, as in Fig. 2, or {b) with the rays from the 



* A lUitonj ofBrilish Starfislies (London, 1841), by Edward Forbes, p. .50. 



t Catalogue of the Briti$h Echinoderm» in the Brilifh Miueum (London, 1892), p. 129. 



