102 THE NAUTILUS. 



gill-filaments, and stand in rows, forming interrupted septa and in- 

 complete, intercommunicating water-tubes. Toward the base of the 

 gill the interruptions are short and the interlamellar connections 

 stand close together, resembling almost continuous septa. Toward 

 the edge of the gill the interlamellar connections are more distant, 

 showing a tendency to fall into transverse rows, but these are rather 

 irregular, and in some places an almost reticulate appearance is 

 presented. 



The female examined is sterile, and thus nothing can be said 

 about the eggs and glochidia. A slide, belonging to the same 

 species, and kindly communicated by Mr. Frierson, shows vertical 

 cross sections through the inner gill of a female, containing eggs, 

 but no glochidia. 



The rest of the soft parts offers nothing remarkable. The foot 

 has a sooty-black color in its distal parts, sharply marked off from 

 the whitish basal parts. 



It is evident that this structure agrees to a remarkable degree with 

 that of the South American genus Hyria, described previously 

 NAUTILUS, 24, Jan. and Febr., 1911, pp. 108 and 114): In fact, 

 practically all the essential features are identical. The South Amer- 

 ican genera D/plodon, Castalina, and Tetroplodon possess the same 

 anatomy, except that in some of them we observe a tendency to 

 form a mantle-connection in front of the brachial opening. 



The only differences I am able to discover in the Australian form 

 are: 1. The anal opening is much shorter and approaches more a 

 circular outline, and, at the same time, the united mantle edges form 

 a much broader membrane between the outer edges, and are broader 

 around the anal, so that is is probable that the ana) of the Australian 

 species was capable of being stretched out as a tubular "siphon," 

 much more pronounced than in the South American forms; 2. An 

 unusual feature is the hole by which the cloacal cavity communicates 

 with the branchial under the bridge, which separates anal and branch- 

 ial openings. This hole is clearly seen in both of my specimens, 

 and does not look like an accidental or abnormal condition. I have 

 not seen anything like it in any South American form. 



The connection of the posterior margins of the palpi probably is 

 of no consequence; there is great variability in this feature in other 

 groups. 



It seems to me that the above differences are important. Of 



