14 



[REP. OF THE "MICHAEL SARS" NORTH 



area of the Faroe- Shetland Channel ("Porcupine" 1869 

 stat. 57, 60° 14' N., 6° 17' W., 1156 m, 0,8° Cel. and 

 stat. 58, 60° 21' N., 6° 51' W., 988 m., -4- 0.6° Cel. and 

 "Knight Errant" 1880, stat. 8, 60° 3' N., 5° 51' W., 988 

 m. -4- 1.56° Cel.). 



Plutonaster agassizi Verrill. 

 (PL 4, figs. 2—4). 



Archaster agassizi Verrill, Amer. Journ., ser. 3 vol. 20, 1880, p. 403 - 

 3 %. Stat. 70, 42° 59' N., 51° 15' W., 1100 m. Temp. 3.7° Cel. 



One specimen, measuring: 



Diameter 154 mm. 



Arm-radius 79 



Disc-radius 24 



Breadth of arm at 4 — 5 dorso-marginal plate 13 



Breadth of paxillary area at same place 7 



Breadth of arm in the middle 10 



Breadth of paxillary area at the same place 4 „ 



Size of madreporic area 2.5 X 6 



Distance of madreporic area from centre of disc 11.5 



Number of dorso-marginal plates 31 — 32 



Number of ventro-marginal plates 30 — 31 



r : R 1 : 3.29 



The marginal plates are very small and high in the 



arm-angles increasing proportionately in length as they 



advance towards the points of the arms, where they are 

 almost quadrate as the following measurements distinctly 

 show : 



1st dorso-marginal plate 2 mm. long, 5 mm. high. 



10th -„- 2.5 „ „ 4 



20th -„- 2 „ 3 



25th -„- 1.5 „ „ 2 



1st ventro-marginal plate 2.5 „ „ 6.5 



10th -„— 3 „ „ 4.5 „ 



20th — „- 2 „ 2.5 „ 



251h -„- 1.5 „ ,, 1.5 „ 



The ventro-marginal plates are furnished with a 

 well-developed conical knob, the height of which equals 

 the length, of the plates. It is wanting, however, in 3 to 6 

 of the outermost plates, as well as in a few of the others. 

 The knob is rudimentary in some plates. Most of the 

 dorso-marginal plates are bare, and only a few of them 

 bear a little rudimentary knob. 



7 to 9 papillae were counted along the free margin 

 of the mouth plates and also 7 to 9 adambulacral papillae 

 of about uniform size. Outside the latter a group of 

 small short papillae were found, the outermost of which 

 corresponded in size and in form to the granules of the 

 actinal plates. This group of secondary papillae was ar- 

 ranged in 2 to 4, most commonly i 3 rows. The arrange- 

 ments were not very distinct, however. No pedicellariae 

 were observed on the actinal face. 



Although Verrill's description of Plutonaster agassizi 

 is far from exhaustive it yet clearly shows that his species 

 is identical with Plutonaster rigidus Sladen, and as this 

 name dates from 1889 while Verrill's is from 1880, the 

 latter has the priority. 1 agree with Koehler in referring 

 Plutonaster granulosus Perrier to PL agassizi. Further 

 PI. intermedins, taken off the Antilles by the "Blake", 

 must be referred to the species under discussion. Perrier 

 states that PL intermedins is distinguished from PL agassizi 

 by the presence of 8 mouth-papillae while the other 

 has 9, by having 7 adambulacral papillae, while there are 9 

 in the other species, by having two rows of secondary 

 adambulacral papillae as against 3 rows in the other form, 

 by having commonly a knob on the dorso-marginal plates, 

 while the knob is wanting in the other form, and finally 

 by possessing 22 — 27 marginal plates, while the other 

 has 31. 



The last-named difference can be of no great signi- 

 ficance, however, as Perrier's type-specimen was a small 

 individual. Nor is the presence or absence of knobs on 

 the dorso-marginal plates a reliable specific characteristic. 

 Perrier writes about the knob-covering on the dorso- 

 marginal plates of PL intermedins: " — — — 



elles portent, en general, un piquant eonique, sauf sur 

 la moitie terminale des bras ou elles sont inermes; ce 

 piquant peut d'ailleurs avorter accidentellement, meme 

 sur les plaques qui sont situees dans l'arc interbrachial" l ). 

 He further says ("Stellerides des dragages du Blake") 2 ) 

 that the dorso-marginal plates of the interbrachial angles 

 at least are furnished with knobs. Verrill remarks on 

 PL agassizi: "In one large series there are among the 

 adult specimens all gradations from those having no 

 marginal spines whatever to those that have a large 

 spine on nearly every marginal plates of both series. 

 Therefore it is useless to recognize varieties on this character 

 like the variety semiarmata of Sladen" 3 ). The specimen 

 under discussion as before mentioned has a knob on some 

 of the dorso-marginal plates. 



The armature of the adambulacral and the mouth- 

 plates does not seem either to afford reliable specific cha- 

 racters. The specimen in question has 7 — 9 papillae along 

 the free margin of the mouth papillae. Thus the number 

 of papillae characteristic of PL intermedins (8) as well as 

 of PL agassizi (9) is found in the same specimens. It is 

 noteworthy, however, that Sladen in his description of 

 PL agassizi s. rigidus uses the expression "about nine 



1 ) Perrier: Echinodermes, Exp. Sci. du "Travailleur" et du "Talis- 

 man, 1894, p. 316. 



2 ) Nouv. Arch, du Museum d'Hist. Natur., ser. 2 tome 6, 1883, 

 p. 251. 



3 ) Proc. U. S. Nat. Museum, vol. 17, 1894, p. 248. 



