122 DISCOVERY REPORTS 



It seems likely that Koehler's Pergamaster tessellatus is at best only a form of incertiis. 

 His 3 specimens were all larger, R being 43, 40 and 35-36 mm. Koehler does not men- 

 tion the prominent subambulacral tubercle which appears to be absent on the proximal 

 plates but can be seen with a lens on the distal plates in figs. 6 and 8, pi. 49 (Koehler, 

 1920). In the type of sytmptonis this tubercle is sporadic on the proximal plates but 

 regularly occurs in the paratype. Koehler's specimens (1920, p. 238, pi. 49, figs. 5-17) 

 were taken at 2 stations: 64° 34' S, 127° 17' E, 1700 fathoms and 64" 32' S, 97° 20' E, 

 no fathoms. 



Type locality. McMurdo Sound, south-west corner of Ross Sea, about 77° S, 

 96-120 fathoms. 



Pergamaster synaptorus sp.nov. 

 (Plate II, fig. 3 ; Plate III, fig. i) 



Diagnosis. Differing from Pergamaster incertiis (Bell) and P. tessellatus Koehler in 

 having the distal 5-7 pairs of superomarginals joined medially, excluding abactinal 

 plates from terminal part of ray. R 45 mm., r 27 mm., br at interradius 28 mm.; 

 paratype measures R 33 mm., r 13-5 mm., br 13-5 mm. 



Description. The precise form and arrangement of the abactinal plates can be 

 determined from the figures. The exposed surface of the plate is flat and is in reality a 

 very low tabulum surrounded by a single series of unequal flat granules, flush with the 

 surface. Koehler uses the misleading term " little plates " for the granules. The adradial 

 row of plates extends to the middle of the fourth superomarginal of type (and to middle 

 of third of paratype) while the radial series continues to middle of eighth superomarginal 

 (sixth of paratype). Beyond this point 5-7 superomarginals meet in the midradial line, 

 those of opposite side, but are usually not accurately paired. Papulae inconspicuous, 

 occupying a broad petaloid radial area. Madreporite variable, small to large, situated at 

 mid r. 



The marginals are bare except for the peripheral series of elongate or squarish granules 

 flush with surface. The plates of the 2 series sometimes correspond, sometimes do not. 

 Superomarginals 13-14 (11-12 in paratype) block-like, broader than long, and forming 

 a rounded border to ray and disk. The second plate is conspicuously larger than first, and 

 thence they decrease very gradually in size along ray. 



The infero marginals form a more abruptly rounded margin and, from the fourth 

 plate on, are in contact with adambulacrals (fifth in paratype). 



The actinal plates of type are completely covered with coarse close-set polygonal 

 granules, but those of paratype have only a peripheral series leaving the centre of plate 

 bare. There are 3 chevrons of these plates to each interradial area. The series adjacent to 

 adambulacrals extends to proximal border of fourth inferomarginal of type (one-half to 

 one plate farther in paratype). 



Adambulacral plates proximally a little broader than long and narrowing on ray 

 proper until the two dimensions are about equal. Furrow spines 2 or 3, subequal, heavy, 

 blunt, sometimes slightly compressed, and about as long as width of plate. Back of these 



