Australian Ilydrolds. 7'6 



In ixrciit years several observers have, following Von Lenden- 

 fekl. admitted the genus Eiccopella, and Fraser. recognising the 

 affinity ot' C caliculafa with Von Lendenfeld's genus, has adopted 

 the name Kncoj/clhi cal/riihifd . No doubt Fraser is right with, 

 regard to the affinity of that species, but if such forms are to be 

 separated from Cdinpaniilarid or Vlijt'ui (as most observers seem 

 inclined to separate them), then they must be referred to Ortliopi/ria. 

 whieh ^\as fai' anterior to Von Lendenfeld's genus. That Eucopdla' 

 should be superseded is the more desirable, since much confusion 

 has been caused by the original association under that name of two 

 quite unrelated forms. 



The most impoi-tant character of the genus Orf/iopi/u/s is the 

 structure of the gonozooid, which, as described by Agassiz, is a 

 very degraded form of medusa, having an umbrella with foui' 

 radial canals, l)ut neither manubrium nor tentacles. There is alsc' 

 a peculiarity of the tropliosome not noticed by any of the earlier 

 observers, namely the distinctly bilateral development of the hydio- 

 theca. which is compressed in the lower half so as to be of an elliptic 

 or iiblong section, while, as a lule, retaining the ordinary circular 

 form in the distal portion. Another prominent characteristic, ap- 

 parently Lummon to all the species, is the variability in thickness, 

 of the hydrotheca-wall, which occurs in individuals not only of the 

 same variety, but also of the same colony. I find this variation in 

 thickness to l)e dependent, to a certain extent, on the position in 

 whieh the hydrotheca is viewed; thus a hydrotheca seen in its 

 broader aspect is not only less tapering downwards, with a wider 

 and riattei- floor, but its wall conuiionly appears distinctly morf 

 thickened than when it is seen in its narrow aspect. In some of 

 the published figures of 0. coin preaxa the thickening of the calycle- 

 wall is remarkably developed. 



In 0. ealicidata the peduncles, which vary extjemely in length, 

 are slender, thin-walled, and twisted into a loose, irregular spiral 

 generally throughout their length, but sometimes with smooth or 

 nearly smooth intervals. Most of the other forms agree in this 

 particulai'. oi- else have the undulations shorter and more pro- 

 nounced. l)ut O. compressff and 0. a/if/u/ata have peduncles whicln 

 are stouter in themselves, and pi-ovided with thicker perisarc. and 

 never exhibit the spiral oi- undulated form found in the other 

 species. Below the pronounced globular segment which occui-s im- 

 mediately under the hydrotheca in all the species, these often have- 

 a distinct oblong segment, and there may be a few constrictions at 

 irregular intervals. 



