ASTEROIDEA 203 



ready to leave the marsupium, but the other eight were quite small, R ranging from 1-25 

 to 2-5 mm. The smallest (6-rayeci) specimen has 3 adambulacral spinelets and 3 oral 

 spinelets per plate. The actinolateral membrane, with 5 spines on either side of each ray, 

 extends conspicuously beyond the border and tip of the ray proper as in Hymenaster. 

 The terminal papilla of radial water tube is large and there are 6 pairs of tube-feet to 

 each ray. 



From this glimpse into the genetics of the species it is evident that the 6-rayed speci- 

 mens are not specifically distinct. It is significant that the majority of the young of a 

 5-rayed parent are 5-rayed; and of a 6-rayed parent preponderantly 6-rayed. It is 

 probable that the 7- and 8-rayed specimens are from 6-rayed rather than from 5-rayed 

 parents (or from 7- and 8-rayed parents). 



Pter aster obscnriis of the north Atlantic, Arctic Ocean and Bering Sea has 6-9 rays. 

 In a large 7-rayed specimen I found two 6-rayed young, ^ and in two adults with 8 rays I 

 found one 9-rayed, three 8-rayed and two 7-rayed young — all three sorts occurring in the 

 same parent. Pteraster obscurus, although aberrant for the genus, seems to be much 

 nearer to Pteraster than to Diplopter aster. 



Perrier's figures oi Pteraster ingouffi, although small, indicate clearly the general habit 

 and crowded tube-feet of Diplopteraster verrucosus. With a lens one can distinguish the 

 two sorts of adambulacral combs. Ingouffi is described as having a slender suboral spine 

 encased in membrane and a fan of 10 oral spines completely webbed. This describes 

 verrucosus exactly, as no other Pteraster of the region has this oral armature. Pt. gibber 

 has the marginal spines united by membrane but the suboral is heavy not slender, and 

 the actinolateral membrane is characteristically narrow — entirely unlike that of m- 



gonffi. 



Type locality. Challenger St. 313. Near the Atlantic entrance to the Strait of 

 Magellan, 55 fathoms, sand; bottom temperature, 47-8° F. 



Distribution. Falkland Plateau, north to latitude 40°, coast of Argentina; south to 

 Navarin Island (Perrier) and Burdwood Bank (Koehler) ; 74-270 m. 



Diplopteraster semireticulatus (Sladen) 



Pteraster semireticulatus Sladen, J. Linn. Soc. Lond. (Zool.), xvi, 1882, p. 195; 1889, p. 475, pi. 75, 

 figs. 5, 6; pi. 77, figs. 5, 6. 

 St. 1562. Off Marion Island, 46" 52' S, 37° 55' E, 99-104 m., 3 specimens. 



The smallest and only perfect specimen measures R 13 mm., r 8 mm., and is therefore 

 for all purposes the same size as the type, the figures of which it closely resembles. This 

 specimen has 4 or 5 adambulacral spines in irregular alternation, the innermost of the 

 series (and sometimes the second in the case of 5 spines) being conspicuously shorter 

 than the others. The supradorsal membrane is semi-transparent. The paxillae have 6 

 or 7 rather long delicate spinelets surrounding a central one, essentially as in the type 

 specimen (Sladen, pi. 77, fig. 5). The tube-feet are crowded, incipiently quadriserial, but 



1 Fisher, 1911, p. 365, pL 105, fig. i. 



