PLATE XXVIII. 
Figs. 1, la. — Sertularia echinocarpa (p. 57). 
Fig. 1. — Portion of a colony ; natural size. 
Fig. la. — Portion of same ; magnified 10 diameters. 
Figs. 2, 2a. — Sertularia catena (p. 58). 
Fig. 2. — A colony ; natural size. 
Fig. 2a. — Portion of a colony ; magnified 10 diameters. 
Figs. 3, 3a, 3 b. — Sertularia producta 1 [ geniculata ] (p. 59). 
Fig. 3. — Portion of a colony ; natural size. 
t 
Fig. 3a. — Portion of same; magnified 15 diameters. 
Fig. 3b. — A hydrotheca, further magnified; showing the striation of its summit, the 
operculum, and the internal projecting ridges. 
1 It has been found necessary to change the name since the Plate was printed off. 
