REPORT ON THE CRINOIDEA. 131 



20. Antedon pusilla, n. sp. (PI. XXIII. fig. 1). 

 Spec ifc formula — A . y . 



Description of an Individual. — Centro-dorsal a low hemisphere bearing about fifteen 

 cirri with some twenty-eight joints, few of whieh are longer than wide, the distal ones 

 with a slioht dorsal keel. 



First radials partially visible ; the second short and oblong with the centre of the 

 distal edge raised to meet the proximal edge of the axillary and form a tubercle. A 

 similar but smaller tubercle at the junction of the first two brachials. All four joints are 

 wall-sided and straight-edged, with the margins of the dorsal surface flattened. 



Ten arms of smooth and elongated obliquely quadrate joints ; syzygies in the third 

 and then generally in the eighth or ninth brachials, with others at intervals of one to five, 

 usually three joints. 



The first pinnule consists of about a dozen elongated joints and is considerably longer 

 and stouter than its successors, which decrease to about the fourth pair and then gradually 

 increase. The two lowest joints of the later pinnules are expanded and trapezoidal, but 

 the following joints are slender. 



Pinnule-ambulacra not plated ; sacculi abundant. 



Colour in spirit, — light brownish-white. 



Spread about 7 cm. 



Locality.— Station 192, September 26, 1874 ; near the Ki Islands ; lat. 5° 49' 15" S., 

 long. 132° 14' 15" E.; 140 fathoms; blue mud. One specimen. 



Remarks. — This is an elegant little form with long arm-joints and the first radials 

 visible externally, both of which characters are frequently indicative of immaturity. But 

 the great development of the genital glands, which are often found as far out on the arms as 

 the sixtieth brachial, seems to negative this idea in the present case. The two characters 

 just mentioned distinguish Antedon pusilla, from Antedon denticulata, from which it also 

 differs in the presence of tubercles on the rays and arm-bases, in the much shorter cirrus- 

 joints, and in the fact that the first and not the third pinnule is the largest. The distal 

 pinnules are very delicate and their two basal joints altogether different from the rest, 

 being expanded and trapezoidal, with their apposed edges much curved, as in many of the 

 Circumpolar species, while there are large and abundant sacculi on both arms and pinnules. 



2. The Acmla-gvo\\\). 



This group includes, at present, only two species, which differ from one another in 

 nearly all the characters of the cirri, arms, and pinnules, but are allied to the Basicurra- 

 group in the presence of a plated disk and of a well-defined ambulacra] skeleton, 

 characters which appear in no other ten-armed Comatulse. 



