Calkins. — Hydroids. 
PLATE 3. 
Fig. 13. Obelia gracilis. Nat. size. a. Hydrocaulus. X 18. b. Hydrotheca 
and hydranth. X 80. c. Gonosome. X 80. 
Fig. 14. Obelia surcularis. Nat. size. a. Hydrocaulus. X 18. b. Hydrotheca, 
hydranth, and gonosome. X 80. 
Fig. 15. Obelia fragilis. Nat. size. a. Portion of hydrocaulus. X 18. b. Hydro¬ 
theca and hydranth. x 80. 
Fig. 16. Obelia dichotoma. Nat. size. a. Hydrocaulus. X 18. b. Hydrotheca 
and hydranth. X 80. c. Gonosome. X 80. d. Distal end of gono¬ 
some. X 80. 
Fig. 17. Selaginopsis cylindrica. Nat. size. a. Portion of pinna. X 80. 
