OF THE MERGUI ARCHIPELAGO. 



105 



has been noticed in describing the species, is most suggestive, 

 and it is quite possible that the almost vertical direction, instead 

 of the usual horizontal one, assumed by the plates and scales 

 may have been necessary whilst the ovarian sac was filled with 

 ova. Knowing how frequently Ophiurans die after parting with 

 their ova, and how thev sometimes suffer from defective amounts of 

 carbonate of lime, I think that it will be worth while for the future 

 to pay attention to the position of the genital plates and scales of 

 Ophiurans which are living under unusual as well as under normal 

 conditions. The anatomical details show that the characters of 

 Opliiopliragmns and AmpJiiura can be combined; and it is very pro- 

 bable that future research will place the genera closer together, or 

 even decide that the first-named must become a subgenus of the 

 latter. The importance of the differences of the internal con- 

 struction of the mouth frames mentioned and excellently illus- 

 trated by Lyman (op. cit., 1 Challenger ' Eeport, pi. xl. fig. 4) may 

 not be so great as is now considered, especially in view of the 

 structure of the particular organs in OphiotJirix variabilis, nob., 

 which will be considered in the next communication. 



The new Ophiocnida with six arms, four arm-spines, and 

 numerous mouth-papilla? is unfortunately founded upon a solitary 

 specimen. Now that attention has been directed to this species, 

 there is a possibility of larger specimens being obtained ; it 

 would be interesting to know whether the sixth limb is always 

 retained. 



The Ophiothrices are numerous in individuals, and there are 

 some very interesting forms amongst them. Almost all have long 

 arms, stumpy, thorn ed disks, and purple or sombre tints, and with 

 some of the glassy spines on the arm broad at the top, oar-shaped, 

 hollow, and compressed. In most of the species hooks are seen 

 very near to the disk. In the majority the tentacles are large, 

 long, and covered with whorls of papillae. There is one species 

 which has given much trouble in classification, for not only are 

 there four fairly marked varieties, but the type has considerable 

 external resemblances to O. galatea, Ltk., whilst the internal 

 structures present shapes which remove the forms from the type 

 chosen by Lyman in illustration of the anatomy of the mouth- 

 frames and arms within the disk, namely O. quinquemaculata, 

 Mull. & Trosch. (' Challenger ' Eeport, pi. xlii. fig. 5). 



The nature of these structural differences will be noticed 

 in the following communication. The species Ophiocampsis 

 pellicula, which can bend its arm in a vertical downward plane 



