238 Transactions. 
a node near the end. The hydrothecae are less close in the distal than 
in the proximal portions of the pinnae, and where a node occurs the 
highest hydrotheca on the lower internode has its border nearly hori- 
zontal. 
The form of the hydrotheca-margin is characteristic, having по trace 
of the three or four emarginations usual in the genus, but being 
perfectly round and smooth, and in general showing no indication of 
the operculum. In this group the operculum is readily detached, yet 
in such species as S. lata, for example, one generally finds its remains 
attached to the hydrotheca-margin (though it is only in well-preserved 
specimens that the four valves are distinct), but in the species before 
us the operculum generally comes clean away, leaving no trace. Only 
Fic. 6.—a, Sertularella edentula n. sp.; х 25. b, Sertularella 
edentula: gonangium ; X about 10. 
here and there can a remnant be found, and then usually insufficient 
to indicate its original form; however, after careful search I succeeded — 
in finding à few specimens intact, all of which were trivalvate, though 
the margin showed no corresponding divisions. 
_ In many of the hydrothecae is found a membranous diaphragm (or 
its remains) situated at a small but variable distance within the margin 
and continuous with a 
could not possibly 
finding а similar struc 
species, s 
