Species ofSpio. 487 



Head proboscldiform, irregularly conical, pointed, light brown. 

 No eyes, nor proboscis. Month inferior. Tentacula two, one inch 

 long, filiform or slightly tapered at the point, white with a red 

 central tortuous vessel, contortile. Bran.chice in a single row along 

 each side of the back, bright red, setaceous, non-retractile, either 

 elevated or laid across when the points of the opposite hairs meet. 

 At the base of each there is a small fascicule of soft white hairs 

 which appear to be also non-retractile. Below these, and divided 

 from them by a line, there is to each segment an elevated trans- 

 verse fold, continued round the ventral surface to the fold of the 

 opposite side by a less elevated and narrower line. These folds 

 are armed with short white retractile bristles on the margin, and 

 when examined with the glass are seen to be beautifully mottled 

 with close-set round spots. Tail stellate. 



This fine species inhabits the same places as the Spio vulgaris 

 which we have described in a preceding contribution, but is much 

 less common. A comparison of the descriptions will at once shew 

 that they are quite distinct j and their specific characters may be 

 thus expressed. 



1. Sp. vtilgaris, BoJy yellowish brown, marked with the red 

 setaceous branchiae: head inversely triangular; eyes four; ten- 

 tacula much shorter than the body. 



2. Sp. viridis. Body green minutely spotted with circular dots ; 

 no eyes ; head conical ; tentacula much shorter than the body. 



This last character is introduced since it serves to distinguish 

 both species from the Sp. seticornis in which the tentacula are said 

 to be nearly as long as the body. I cannot refrain from remarking 

 how admirably the structure of these worms is adapted to enable 

 them with ease and velocity to ascend and descend in the deep 

 holes which they inhabit. 



Class. Vermes. Lamarck. 

 Ord. MoLLAssEs. Id. 

 Gen. Plan ARIA. Linn. 

 This is a very heterogeneous genus, the receptacle at present of 

 all soft external worms. The three species we intend to describe 



