Sertularia. 



Z. HYDROIDA. 



129 



Polypidom 3 or 4 inches high, rigid, pinnate, lanceolate, dusky or 

 blackish-brown, varnished. Stalk straight, compressed, jointed, with 

 a series of alternate cells on each side : pinnae alternate, close, bifa- 

 rious, several originating from each space between the joints of the 

 stalk, simple, narrow at their origins, filiform, often gangrened at 

 the apex. The cells are arranged in a close row along each margin, 

 and directed alternately to opposite sides (Fig. 13) ; they are small, 

 ovato-tu bular, short and adnate with a wide mouth having a small 

 tooth on the outer edge. Vesicles unilateral, superior, elliptical or 

 orate, sub-pedicellate, smooth. 



Fie/. 15. 



To this description, derived from specimens furnished by Messrs 

 Bean and Embleton, I append that of Pallas, for Milne-Edwards 

 denies the identity of his nigra with the British species (^Lcim. Anim. 

 s. Vert. 2de edit. ii. 155) ; for which in my opinion there are no sufiS- 

 cient grounds, but a comparison of the descriptions will enable every 

 one to decide for himself. " Radices sunt tubi intestinuliformes, lu- 

 tescentes, implexi, usque ad pinnarum originem assurgentes. Stit'ps 

 ad summum quadripollicaris, simplex, pennata, sublanceolata, testaceo 

 nigra et tenuior molliorque quam tubuli radic antes. Rachis stirpis 

 est tubulus crassitie fere calami avenacei, compressus, e planiusculis 

 lateribus, et ipsis denticulatis, pinnas proferens. Pinnce s. ramuli 



I 



