450 M. C MereschkoAvsky on new Hydroida. 



Sertularella pinnata, S. F. Clarke. (PI. XVII. fig. 23.) 



Sertulai-ella pinnata, S. F. Clarke, Scient. Results Explor. Alaska, 1876, 

 vol. i. p. 22, pi. Yi. figs. 28, 29. 



I think I may say that this is one of the prettiest hydroids 

 hitherto described. It was described in 1876 by Mr. S. F. 

 Clarke ; and his description is so perfect that I can only add 

 very little to complete it. The collection of the Academy 

 possesses a very considerable quantity of this species, among 

 others also coming from Unalaschka, where it appears to be 

 very abundant. The hydrotheca? are often bent in the middle, 

 forming a fold, although this fold is also frequently wanting. 

 Sometimes, although rarely, the arrangement of the hydro- 

 theca3 becomes normal, so to speak ; i. e. it does not affect a 

 uniserial mode. As Mr. Clarke has not given a figure of the 

 whole colony, the general appearance of which is very charac- 

 teristic and pretty, I think it desirable to give one (PI. XVII. 

 fig. 2o) representing a colony with gonophores. 



EXPLANATION OF THE PLATES. 

 Plate XVL 



i'V^. 1. Selaginopsis triserialisj 8p. n. : a colony, of the natural size. 



Fig. 2. A portion of a branch of the same species, enlarged 25 diameters, 



and drawn with the camera lucida. 

 Fig. 3, Selaginopsis jnnnata, sp. n. : a colony, of the natural size ; per, a 



part of the hydrorhiza in the form of a membrane. 

 Fig. 4, A portion of a branch of the same species, enlarged 25 diameters ; 



drawn with the camera lucida. 

 Fig. 5. Selaginopsis pacijica, sp. n. : a colony, of the natural size. 

 Fig. 6. A portion of a branch of the same species, enlarged 25 diameters; 



drawn with the camera lucida. 

 Fig. 7. A gonotheca of the same species. 



Fig. 8. Selaginopsis thuja, sp. n. : a colony, of the natural size. 

 Fig. 9. A system of branches of the same species, consisting of six 



branches. 

 Fig. 10. Hydrotheca of the same species, enlarged 50 diam. ; drawn with 



the camera lucida. 

 Fig. 11. Selaginopsis ochotensis, sp. n. : a colony, of the natural size. 

 Fig. 12. A system of six branches of the same species, of the natural size. 

 Fig. 12 a. A gonotheca belonging to the same species. 



Plate XVII. 



Fig. 13. Selaginopsis decemserialis, sp. n., var. gracilis : a colony, of the 



natural size, representing a variety of the species distinguished 



by its cylindrical form and shorter branches. 

 Fig. 14. A* system of three branches belonging to the typical form of this 



species, natural size. 

 Fig. 15. A portion of a branch of the same species, enlarged 25 diameters, 



drawn with the camera lucida. 

 Fig. 16. A gonotheca belonging to the same species. 



