120 CAST ALIA. 



water dissolves out the same pink colour as is taken up by 70 per cent, alcohol. The 

 addition of a little alcohol to the sea- water containing the living animal causes the mucus 

 so abundantly secreted by the large dorsal cirri to become purplish. The alcoholic 

 solution is deep reddish -brown by transmitted light, but shows a blue fluorescence when 

 seen from above. These tints remained for several weeks, but gradually faded into a 

 yellowish-brown colour." Yet in pure sea-water it is by no means difficult to keep 

 Ophiodromus alive for a long time, and clayey mud is not deleterious. It swims 

 through the water with more grace and even greater agility than Nephthys, but breaks 

 into fragments if much interfered with. Even the separated posterior end keeps up a 

 constant and violent motion — darting about in various directions for some time. While 

 rupture of the body thus frequently occurs, yet reproduction of the posterior end readily 

 takes place. 



Delle Chiaje's description 1 (1841) is: Head with four tentacles, furnished with a 

 proboscis ; body yellowish-brown, banded transversely with white ; tail with two cirri ; 

 tentacular cirri on six segments. His figures bear a close resemblance to the present 

 species, though the identification is not free from doubt. On the whole it is probable 

 that the northern form is only a variety of the southern, and it may be that it is a com- 

 mensalistic species on Astropecten and Luiclia, though this has not actually been observed. 



The Hesione Steenstrupii of De Quatrefages (1865) from Guettary seems to approach 

 this form very closely. 



The Oxydromus fuscescens of Marenzeller 2 (1875) from the Adriatic appears to be 

 very closely allied. 



Levinsen (1883) states that Tauber considers this the Stephania fiexuosa of Delle 

 Chiaje, but he differs from him. 



Genus XL. — Castalia, Savigny, 1820. 



Head somewhat square, with four eyes obliquely arranged. Tentacles two ; palpi 

 biarticulate. Tentacular cirri two to three pairs, filiform and long. Body scolopendri- 

 form; proboscis firm, barrel-shaped, aperture papillose, with or without two thickened 

 ventral ridges (so-called jaws). Foot biramous ; superior division minute with or without 

 simple dorsal bristles; inferior division large with compound (falcate) bristles, the 

 terminal pieces being bifid. Dorsal cirri longer than the ventral. 



This genus was established by Savigny (1820) to include such forms as the Nereis 

 rosea of 0. Fabricius. All he states is that this species, while agreeing generally with 

 the heterogeneous assemblage of forms under his Nereides, differs in that the tentacular, 

 dorsal, and anal cirri are long and smooth, and that there are two divisions in the foot. 



(Ersted 3 describes the palpi as like the tentacles and non-articulate ; four tentacular 

 cirri ; four eyes ; minute, slender, pellucid, and edentulous maxillge ; pinnse two, superior 

 minute, inferior large trilobed, one spine in superior, three in inferior division ; dorsal 

 bristles capillary, ventral falcate. 



1 < Descriz./ v, p. 103, Taf. 109, fig. 8. 



2 ' Sitzb. d. K. Akad. d. Wiss./ i Jahrg. 1875, p. 15, Taf. ii, fig. 1 (sep. copy). 



3 ( Annul. Dan. Consp./ p. 23. (1842.) 



