190 CEYLON PEARL OYSTER REPORT. 



that during life the animal may have had a short posterior projection which has 

 become retracted. The difference, however, between the British Museum specimen 

 and the Ceylon specimen is, Professor Herdman informs me, not now very marked in 

 this respect. 



There are five series of pedicels ; each series consists of a double row on the 

 " neck," but on the wider portion of the body each series of the trivium consists of 

 about four rows, while each series of the bivium consists of two or three rows. At 

 the posterior end the series are not so well defined, each having only one or two 

 rows of pedicels. There are also one or two pedicels on the interambulacra. 



The sucking discs of the pedicels are dark brown or almost black in colour, thus 

 being easily distinguished on the lighter skin. 



There are no anal teeth. The tentacles have been cast off. 



Deposits: The spicides (Plate I., figs. 2 to 4) are of one kind and are numerous. 

 Typically they are like a cross having four arms in one plane and with two additional 

 arms arising at right angles to this plane at the junction of the four arms. There 

 are many variations of this, some appearing like a short rod covered with many spines. 



The calcareous ring (Plate I., fig. 5) is 5 millims long and consists of ten pieces. 

 The inter-radials are small and are separate from the radials. The radials are 

 bifurcated posteriorly, and the bifurcations are composed of several small pieces. 



There is one stone canal and one Polian vesicle. 



The retractor muscles are remarkably long, and are attached to the longitudinal 

 muscles halfway down the body. 



Distribution : New Zealand, Ceylon. Now recorded from the Indian Ocean for 

 the first time. 



Cucumaria irabricata (Semper). 



Ocnus imbricatus, Semper (2), 1868. Ocnus javanicus, Sluiter, 1880. Ocnus typicus, 

 Theel (7), 1886. 



Ten specimens from (1) Pearl Banks (Stn. LXVL), Gulf of Manaar, (2) West of 

 Kaltura (Stn. XLI1L), 22 fathoms, and (3) Back Bay, Trincomalee (Stns. XX. and 

 XXI.). Lengths varying from 20 millims. to 50 millims. 



Although Theel in his " Challenger" report retained the genus Ocnus, he 

 expressed some doubts as to its validity. Ludwig believed that the three forms 

 0. imbricatus, 0. javanicus, and 0. typicus were identical, and in his Holothurians 

 of Bronn's " Klassen und Ordnungen des Thierreichs" he placed them all in the 

 genus Cucumaria, under the name C. imbricata. 



Eight of the Ceylon specimens I identified as Theel's species 0. typicus, and the 

 other tw r o I considered at first to be Sluiter 's species O. javanicus. But except for 

 some slight differences in the calcareous ring, in the arrangement of the pedicels, and 

 in the scales and colour of the bodv, the two forms appear \r> be very similar. So, on 

 the whole, I now think it best to unite them. 



