370 ECHINODERMS OF THE BRITISH ISLES 



2. Short, nearly ovoid forms ; lateral appendages throughout nearly 



the whole length of the body ..... 3 



More or less elongate forms ; lateral tube-feet not reaching the 



anterior end ........ 6 



3. Veil very small, only a basal web uniting the four anterior, small 



papillae ; a third, smaller pair placed behind the veil. Nine lateral 

 tube-feet on each side. Deposits large, robust, with relatively 

 short, very thorny outer projections (" Talisman " Holoth., 

 p. 426, Pis. XIII. 7-9, XIX. 15-23) . P. porcellus Perr. 



Veil well developed or very large ..... 4 



4. Veil not forming a large anterior hump or overhanging brim ; 



the two pairs of papillae united by a web leaving only the tips 

 free ; a single papilla at each side at base of veil. Five pairs of 

 large tube-feet on each side, arranged in groups of 2 anterior 

 and 3 posterior. Deposits small and delicate, with few 

 spines, arms but slightly bent {"'Monaco'', xxi., p. 41, 

 Pis. VI. 11-15, VIII. 16, 18) . . . P. obsoleta (Her.) 



Veil forming a large anterior hump or overhanging brim . 5 



5. Veil deeply clef^- in four parts ; 2 pairs of small papillae at 



base of veil. Six large tube -feet on each side and 2-3 very small 

 ones at posterior end. Deposits of the usual type, large and 

 strongly spinous (" Challenger " Holoth., i., p. 42, PI. X. 3-4 ; 

 ''Mich. Sars'' Echinod., p. 6, PI. III. 3-5) P. Wyvillii Theel 

 Veil not cleft, forming a large anterior brim, which continues 

 backwards along edge of body ; apparently no small papillae 

 at base of veil. Seven tube-feet on each side, the two posterior 

 small. Deposits wdth nearly straight and smooth arms ; 

 outer projections longer than arms {'"'Monaco'', Ixvi., p. 86, 

 Pis. I. 31, IX. 1-2) .... P. /oZmcea (Her.) 



6. Veil cleft to the base in the middle, thus formed by two lateral 



halves. Nine tube -feet of nearly equal size on each side, in the 

 posterior two -thirds of body ; three small appendages on posterior 

 end, united by a web. Deposits ventrally with much shorter 

 outer projections than dorsally, finely spinous {"Monaco", 

 vi., p. 12, Pis. I. 4, II. 5) . . .P. azorica v. Marenz. 



Veil divided into four parts or undivided .... 7 



7. Veil deeply incised, divided into 4 parts ; 2 pairs of small 



papillae at base of veil. Five large tube-feet on each side of body 

 in the posterior half, and 2-3 very small at posterior end. 

 Deposits wuth outer projections slightly shorter than arms, 

 spiny (" Mich. Sars " Echinod., p. 7, PI. I. 4-6) 



P. ferruginea Grieg 

 Veil not divided, only with serrate margin ; one pair of small 

 papillae at the base of the web. Five large tube -feet on each side, 

 and two pairs much smaller at posterior end. Deposits with 

 outer projections as long as the arms, which are very finely 

 spinous or nearly smooth (" Ingolf " Holoth.) 



P. islandica Deichm. 



