378 SCALISETOSUS ASSIMrLIS. 



Synonyms. 



1875. Hermadion assimile, Mcintosh. Invert, and Fish., St. And., p. 117. 



1876. „ „ idem. Trans. Zool. Soc, ix, 387 and 400, pi. lxx, f. 4—6. 

 1886. „ „ Harvey-Gibson. Yerm. Liverp., 151 and 348. 



1891. „ „ Hornell. Op. pit., 237. 



Habitat. — First found at St. Andrews, by my sister; afterwards on the west coast of 

 Ireland, in 80 fathoms, eighteen miles west of Skellig, by Dr. Gwyn Jeffreys ; south 

 of England and off the Spanish coast in the ' Porcupine ' Expedition. Oommensalistic 

 on Echinus esculentus (Harvey-Gibson). 



Head has a similar outline to that in the former species, and in the preparations is 

 about as long as broad. The anterior lobes are smoothly rounded, and the eyes have the 

 same position and proportions, the larger anterior pair showing lenses. Both are 

 visible from the dorsum, and have a long portion of the head in front. The median 

 tentacle arises between the rounded anterior lobes, is long, smooth, slightly dilated 

 below the filiform tip, and minutely dotted under a low power, though this seems to 

 disappear in the mounted preparations. The lateral tentacles are short (in spirit) and 

 slightly enlarged below the filiform tip. The palpi are quite smooth. The tentacular 

 cirri are also smooth, slightly enlarged below the extremity, and are shorter than those 

 of 8. communis. 



Body somewhat narrow, about f inch or upwards in length, very slightly tapered in 

 front, and very gradually diminished posteriorly. It is distinguished by a brownish- 

 black median band, which commences behind the head and continues to the tail. It is 

 widest towards the posterior part of the proboscidian region, though even there occu- 

 pying less than a third of the arch of the dorsum. In the preparations a darker band 

 occurs at the segment- junction, and a pale belt just in front. The ventral surface is 

 pale. The segmental eminences are prominent, but special papilla3 could not be 

 made out. 



Attached to the ventral surface were several long Pedicellarise, probably from an 

 Echinus, and some were also fixed to the feet. 



Proboscis. — The proboscis seemed to agree with the preceding in structure, but in 

 the preparation the papillse were somewhat clavate instead of acute. 



Scales (Plate XXXIII, fig. 6), fifteen pairs, even more delicate and transparent 

 than in the previous form, and similar in shape. The cuticle of the inferior surface is 

 minutely dotted throughout as in S. communis. The outer and posterior borders have 

 short clavate cilia, less numerous than in the latter, and they also occur on the neigh- 

 bouring surface. The finely branched nerves arise from a similar ganglion at the 

 posterior border of the scar. 1 



Feet. — In looking at the feet of the two species from the dorsum a decided difference 

 is observed in the terminal region of the ventral division, which in 8. assimilis (Plate 

 XXX, fig. 15) is somewhat blunt and rounded, whereas it is acute in 8. communis. In 

 profile this divergence is more pronounced, since the fleshy part of the dorsal lobe is 

 larger in 8. assimilis, and the spine has a broader covering, and instead of the acute cone 



1 The thickenings observed in these scales do not appear to indicate papillas in all cases. 



