Dr. Gwyn Jeffreys on Arctic Post-tertiary Fossiln. 229 



EXPLANATION OF THE PLATES. 

 Plate V. 



Fig. 1. Tellma solidnla yvith. a colony of Monubrachium pca-cisitiwi, mag- 

 nified : a, a yoimg Proto/ti/dra-like specimen ; b, gonopliore. 



Fiff. 2. Three specimens of full}' matm-ed liydrantlis and a gonopliore, 

 more magnified : a, the oral orifice of the body ; b, its single 

 tentacle ; c, chitinous membrane, covering the ccenosarc and 

 forming a continuous hydrorhiza ; d, a shghtlj' developed hydro- 

 caulus; e, gonopliore. 



Fiff. 3. A gouophore pressed by a covering-plate : a, chitinous membrane 

 covering the medusa; h, umbrella of the medusa; c, the short 

 pedicle of the gonopliore ; d^ d-, a pair of sexual sacs ; d^ d^ iP cP, 

 the same ; d\ sac only, the other is omitted ; r/', g\ y^, g^, the 

 four radiating canals;/', ,P.,f\ /*, the four principal tentacles, 

 into which are continued the radiating canals, and between which 

 are disposed the other twelve tentacles. 



Fig. 4. A gonopliore less compressed by a covering-glass : «'«'-, two radi- 

 ating canals, very distinctly seen ; V, b^, P, 6', four tentacles, the 

 first developed ; c, chitinous membrane. 



Fig. 5. A gonophore with the eight sexual sacs seen through the 

 coverings. 



Fig. 6. The same gonophore seen from above ; the sLxteen tentacles are 

 seen. 



(All the figures excepting figs. 1 and 2 are drawn by the camera lucida.) 



Plate VI. (dra\vn by the camera lucida). 



Figs. 7, 8, 9, 10. Transverse sections of the hydianth. 



Fig. 11. A thread-cell. 



Fig. 12. Transverse section of a gonophore in an advanced state of deve- 

 lopment, with the umbreDa, the four radiating canals, and the 

 eight sexual sacs. 



Fig. 13. Transverse sections of the same gonophore, but at a higher part 

 of it, where the original four sacs are not yet quite divided lon- 

 gitudinally into eight, a and b are the two opposite sacs at a 

 more advanced stage of longitudinal division than the two other 

 sacs. 



Fig. 14. The same fi'om another gonophore, not yet so mature as in figs. 

 6, 7, but made at the same part of it as the section presented in 

 %• 6. 



Fig. 15. Polyserias Htncksii, nat. size. 



Fig. 16. The same, magnified. 



XXXI. — The Post-tertiary Fossils procured in the late Arctic 

 Expedition ; with Notes on some of the Recent or Living 

 Mollusca from the same Expeditio7i. By J, GwYN 

 Jeffreys, LL.D., F.R.S.* 



Mk. Edgae Smith, of tlie British Museum, has published, in 

 the ' Annals and Magazine of Natural History ' for this month 



* Communicated by the author, and read at the Plymouth Meeting of 

 the British Association, 20th Aug. 1877. 



