ATLANT. DEEP-SEA EXPED. 1910. VOL. III.) 



ECHINODERMATA 



13 



a specimen of which was taken by the "Talisman" off the 

 west coast of North Africa must likewise be referred to it 1 ). 

 The agreement between these species is clearly demon- 

 strated by comparing Perrier's and Verrill's figures. 2 ) I 

 ought to state that pedicellariae are wanting in Verrills 

 drawing of the specimen, while Verrill himself makes 

 mention of such. The main difference between these forms 

 is then that the pedicellariae between the ventro-marginal 

 plates are wanting in Benthopecten spinosus (Pararchaster 

 armatus). But it is difficult to determine how constant 

 this character is, as only one example of Perrier's species 

 exists. Most probably it is very variable, however, as 

 indeed indicated by that very specimen. The number of 

 pedicellariae on the left side of the arms was 1 to 2 with 

 a rudimentary third on one arm, on the right side 1 to 3. 

 Arm a had 5 pedicellariae, b 4, c 3 and a rudimentary 

 fourth, d 3 and e 3. Most probably Mortensens Parar- 

 chaster nov. sp. (P. fisheri Perrier aff.) from the slope 

 south of Iceland ("Thor" 1903 stat. 164) 3 ) must be refer- 

 red to Benthopecten spinosus. 



The "Challenger" has taken Benthopecten spinosus 

 off the east coast of North America between 37° 25' and 

 42° 8' N., at 2269—3111 m., temp. 2.33—3.33° Cel., as 

 well as off Portugal. According to Verrill it is distributed 

 along the east coast of North America between 35° 10' 

 and 42° 47' N., from 1319—3698 m., but being most 

 common at a depth of 2200—2900 m. It is further 

 recorded by Verrill from the Mexican Gulf, 2334—2617 m., 

 and from Jamaica, 2999 m. The "Thor" took it south 

 of Iceland (stat. 164, 62° 10.8' N., 19° 36' W., 2094 m., 

 temp, at depth of 1850 m., 2.75° Cel.), the "Helga" off 

 the west coast of Ireland (51° 22' N., 12° 41' W., 1797 m.) 

 and the "Talisman off the west coast of North Africa 

 (1883, stat. 73, 25° 39' N., 18° 26' W., 1435—1056 m.). 

 Benthopecten spinosus thus appears to be a deep-sea 

 species whose distribution includes the entire northern 

 part of the Atlantic and the habitat of which is restricted 

 to the waters whose temperature is not below 2.33° Cel. I 

 may mention for comparison with the temperatures given 

 above, that the "Albatross" in 1883 found a bottom 

 temperature not lower than 2.78 D within the range of 

 distribution of this species. 



J ) E. Perrier: Echinodermes, Exp. Sci. du "Travailleur" et du 

 "Talisman", 1894, p. 263, tab. 20, fig. 2. 



=) Transact. Connecticut Acad., vol. 10, 1900, p. 217, tab. 30, 

 fig. 7 a. 



3 ) Schmidt: Fiskeriundersogelser ved Island og Faeroerne i som- 

 meren 1903 (1904) p. 24. 



Plutonaster bifrons Wyville Thomson. 



Archaster bifrons Wyville Thomson, The Depths of the Sea, 1873, 

 p. 122, figs. 17 and 74. 



10 /4. Stat. 4, 49' 38' N., 11° 35' W., 923 m., sand and mud, 

 temp. 9.2°Cel. One specimen. 



Vs. Stat. 24, 35' 34' N„ 7° 35' W., 1615 m., yellow mud, temp. 

 8° Cel. 15 specimens. 



Vs. Stat. 25 A, 35° 36' N., 8° 25' W., 2300 m„ yellow mud. 

 Two smaller specimens. 



Vs. Stat. 25 B, 35° 46' N., 8 16' W., 2055 m., yellow mud. 

 Four smaller specimens. 



23 /o Stat. 41, 28° 8' N, 13 : 35' W., 1365 m., yellow mud, temp. 

 6° Cel. 13 specimens. 



27 /7. Stat. 95, 50° 22' N„ 11° 44' W., 1797 m., temp. 3.5° Cel. 

 17 specimens. 



Vs— Vs. Stat. 101, 57° 41' N., 11° 48' W., 1853 m., hard clay, 

 temp. 3.3° Cel. Common. 



Vs— 'Vs. Stat. 102, 60° 57' N., 4° 38' W., 1098 m., dark sand 

 and clay, temp. -5- 0.9° Cel. A very defective and macerated 

 specimen, which had most likely remained in the trawl from stat. 101. 



The two smallest (stat. 25 A) and two of the largest 

 specimens (stat. 101) measured: 



Arm-radius 33.5 mm. 37 mm. 92 mm. 97 mm. 



Disc-radius 8 „ 11 „ 18.5 „ 19.5 „ 



Number of dorso- 



marginal plates .. 25 „ 26 „ 37 „ 38 „ 



r : R 1 : 4.19 1 : 3.36 1 : 4.97 1 : 4.97 



The proportions of r : R varied between 1 : 3.36 and 

 1 : 4.47 in 10 specimens with an arm-radius of up to 

 55 mm. in length, but in two specimens only the pro- 

 portion exceeded 1:4.2. In 10 specimens with an 

 arm-radius exceeding 70 mm. the proportion varied 

 between 1 : 3.81 and 1 : 4.97, but in one individual only it was 

 less than 1 : 4. The relative length of the arms is subject 

 to great individual variations, thus the smaller of the two 

 specimens from stat. 25 A. had proportionately the lon- 

 gest arms, and in three specimens with an arm-radius 

 of 45 mm. the proportion r : R varied between 1 : 4.09 

 and 1 : 4.74. But such individual variations apart from 

 the measurements clearly demonstrate that the relative 

 length of arms in Plutonaster bifrons increases with the 

 age. 



Colour in life, reddish violet. 



Plutonaster bifrons is one of the most widely distri- 

 buted starfishes of the East Atlantic. It is known from 

 numerous localities between Cape Verde Is. and the 

 Faroe-Shetland Channel or from 19° 12' to 60° 21' N., 

 leaving out the doubtful find at stat. 102. It is besides found 

 in the Mediterranean. The bathymetrical distribution is 

 from 106 to 2489 m. It is a true warm-water species 

 which was, however, captured three times in the cold 



