REPORT ON THE CRINOIDEA. 135 



Ten arms. First brachial almost oblong ; the second bluntly triangular, with a large 

 lateral process bearing the pinnule-facet. The next few segments each have a process of 

 the same kind, but gradually decreasing in size. Arm-joints after the tenth, triangular, 

 as long as wide, and slightly overlapping, but more quadrate towards the end. Syzygia 

 in the third and beween the tenth and fourteenth brachials ; others at intervals of two 

 to five, usually three, joints. 



The first two pairs of pinnules have twenty or more short joints, the first of which is 

 much expanded dorsally and the next two slightly so. This expansion gradually dies 

 away in the following pinnules, which increase in size, becoming stiff and rod-like, 

 and composed of long cylindrical joints, after the first two, which are laterally compressed. 



Disk and brachial ambulacra much plated. Covering plates of the pinnule- 

 ambulacra supported on a well-developed limestone band, which is not clearly divided 

 into side plates ; the sacculi concealed by it are very large and closely set. 



Colour in spirit, — yellow or yellowish-white, with occasional brown or purplish bauds. 



Disk 6 mm. ; spread about 1 6 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. Four specimens. 



Remarks. — This is a singular species in many ways and is readily distinguished by 

 the characters of the lower arm-joints and of the pinnules which they bear. The broader 

 end of each joint projects considerably from the general lateral line of the arm, so as to 

 form a large pinnule-facet ; and the dorsal part of the first pinnule-joint is expanded into 

 a large curved plate which covers in this facet. This plate, which i3 well shown in PI. X. 

 fig. 2a, is sometimes so large that the whole arrangement looks as if it were a malformation 

 due to the action of an encysting Myzostoma which had taken up its abode in the pinnule- 

 socket. It is largest in the first two pairs of pinnules, the remaining joints of which are 

 relatively quite short, especially in the first pair (PL X. fig. 2a), but by the fourth pair 

 (PI. X. fig. 2b) the two basal joints are less expanded, though the third is slightly so, 

 while the following joints are much longer and somewhat carinate. In the middle and 

 distal pinnules this tendency disappears and the two low T er joints have the usual somewhat 

 flattened appearance. 



The lateral projection of the arm-joints to form large pinnule-sockets is a point of 

 some interest because it occurs in some forms of the Jurassic Antedon costata, as for 

 example that figured by Walther on taf. xxv. fig. 6 of his memoir. He describes the 

 arm-joints as follows " Das dickere Ende tragt einen dorsal en Knoten und einen seitlichen 

 Fortsatz zur Insertion der Pinnula." 1 



The sacculi are fairly developed on the arms of Antedon discoidea, and in the pinnules 

 they are large and extraordinarily abundant. They are covered, however, by the 



1 Loc. cit., p. 172. 



