148 Dr. Johnston on British Nereides. 



rior ramus of the foot pointed on the dorsal aspect, rather longer 

 than the cirrus ; branchise none. (Plate IX. tig. 1 — 9.) 



Nereis alba, Midi. ZooL Dan. Prod. 217. Zool Dan. tab. 62. fgs. 6, 

 7. Aud. et Edw. Lift. ii. 243. Txirt. Gmel. iv. 89. Bosc, Vers, 

 i. 172. 



Hab. In sandy places between tide-marks under stones. Berwick 

 Bay, not uncommon. 



Desc. Body vermiform, round, or rather somewhat flattened on 

 the ventral surface, tapered anteriorly to a sharp point, less ta- 

 pered at the tail, 2^ inches long, smooth, indistinctly annular, of 

 a yellowish- white colour, stained with the contents of the intes- 

 tine, and marked with a red vessel down the back. Head cor- 

 nuted, the apex surmounted with four minute «n/ew»« only visible 

 wdth a magniiier. Proboscis very large, faintly striate in a lon- 

 gitudinal direction ; the teeth brownish-black, corneous, falcate, 

 divided into three processes at the base, inserted into a sort of 

 tubercle forming a square round the plain oral aperture. Seg- 

 ments very narrow, equal and numerous. Feet papillary, obscurely 

 biramous, obtuse, pointed above at the outer angle ; the ciiTi 

 short, the inferior almost obsolete : bristles colo\u*less, jointed near 

 the apex ; the spines straight, setaceous, pellucid. Anal segment 

 rounded, apodal, terminated with two minute styles, which are 

 frequently cast off in the animal's struggles. 



Ghjcera alba lives under stones, sometimes buried in the gravel 

 or sand, but the worm never penetrates far below the surface. Its 

 motions in the water and in the sand are slow, but when irritated 

 the contortions of the body are violent, and it very often twdsts 

 itself so as to form a short spiral column, as we have attempted 

 to show in the first of our illustrative figm-es. 



Sa\dgny considers his G. unicornis to be identical with the Nereis 

 alba of Miiller. It is more probable, however, that the British 

 species is the same as the Norwegian ; the more especially as 

 there is nothing in the description to create any doubts of their 

 identity. The G. unicornis is remarkable for its want of jaws, 

 affording a striking proof that organs of vast importance in the 

 higher classes are here only of secondary consequence, and do 

 not even aff"ord a good generical character. 



Plate IX. fig. 1. Ghjcera alba, natural size, and in a favourite position. 

 Fig 2. The same, with the proboscis protruded. Fig. 3. The head mag- 

 nified. Fig. 4. A view of the proboscis fully extruded. Fig. 5. The apex 

 of the proboscis viewed in front to show the jaws. Fig. 6. Three views of a 

 jaw detached and magnified. Fig. 7. A side-view of a foot from near the 

 middle of the body slightly compressed. Fig. 8. A view of two feet from 

 above. Fig. 9. A bristle highly magnified. Fig. 10. The tail magnified. 



[To be continued.] 



