EXPLANATION TO PLATE XXI. 



FIG. I. ,S' ( rtiiliiri-llu }niltt:nniiin (Klli. ami Solander). Part of branch (enlarged). 



L'. Sertularella polyzanias. Gronangium (enlarged). 



:!. XfHiiliii'fllii f/iniMi (Allman). Part of branch from Allinan's type (enlarged!. 



4. Si-ftiiliiri'llii rliiiiKii. Enil nf hyilriithc'ca, shoxvinj; operculum, fnnn AlhiiMii's tyjif (irreatly 



5. Xfi'tnliii'fllii fuiiii>li:i<t Xuttiiij;. Part of branch (enlarged). 



II. Si'iiuliii'i-llii i-uiii/i/f.rii. Kml nf hyclmtlicca, shmviiif; upcrculiiiii I'-'rcatly enlarged). 



7. Sertularella complexa. Gonangium (enlarged). 

 s, (t. Si-rliiliifi-lln i-ii,-ii/i/i.i-ii. Gonangia viewed from above, showing teeth (enlarged). 



10. SiTliiliin-llii /liniiiiln Clark. Part of colony with 'jonantria (enlarged). 



11. Serlulardlapinnata. Part of branch, front view (enlarged I. 

 1'2. Si-rliiluffllii /ilannlii. Single hydrotheca (greatly enlarged i. 



