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



EXPLANATION OF THE PLATES. 

 Plate V. 



Fig. \. TelUna solidula ■with, a colony of Monobrachium par asittim, mag- 

 nified : a, a young Protohych-a-like specimen ; b, gonophore. 

 Fiff. 2. Three specimens of fully matured hydranths and a gonophore, 

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

 tentacle ; c, chitinous membrane, covering the coenosarc and 

 forming a continuous hydrorhiza ; d, a slightly developed hydro- 

 caulus; e, gonophore. 



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

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

 pedicle of the gonophore ; d^ d'^, a pair of sexual sacs ; d^ d'^ (f e?*, 

 the same ; cP, sac only, the other is omitted ; (7', ^^, y^, (f, the 

 four radiating canals;/', J^^f^, f > the four principal tentacles, 

 into which are continued the radiating canals, and between which 

 are disposed the other twelve tentacles. 

 ■ Fig. 4. A gonophore less compressed by a covering-glass : a^d^, two radi- 

 ating canals, very distinctly seen ; i', ft^, 6', b^, 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 sixteen tentacles are 

 seen. 



(All the figiu'es excepting figs. 1 and 2 are drawn by the camera lucida.) 



Plate VI. (drawn by the camera lucida). 



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



Fig. 11. A thread-cell. 



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

 lopment, with the umbrella, 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 from another gonophore, not yet so mature as in figs. 

 0, 7, but made at the same part of it as the section presented in 

 fig. 6. 



Fig. 15. Polyscrias Ilincksii, 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 Expedition. By J. GwYN 

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



Mk. Edgar Smith, of the British Museum, lias pubb'-shed, in 

 tlie ' Annals and ]\lagazinc of Natural History ' for this month 



• Communicated by the author, and read at the Plyiuouth Meeting of 

 the British Association, 20th .Aug. 1877. 



