Dr. Johnston on the British Aphroditacea. 439 



the co-existence of superior cirri and scales on the same foot. 

 The body is elongate, depressed, almost linear, and formed of 

 numerous segments. The disposition of the cephalic extre- 

 mity is singular ; for the head, in place of being exactly termi- 

 nal, is overtopped by the first pair of feet, which are lodged 

 underneath it and more or less approximated to the mesial 

 line. In our native species there are three cranial tentacula, 

 but in a foreign species the odd one is wanting, and the lateral 

 are always small and lie upon the peduncles of the first feet. 

 The palpi on the contrary are long, and are placed outside and 

 under these feet, of which the two terminal cirri are pointed 

 forwards and may be mistaken for true antennae. There ap- 

 pear to be no eyes. The mouth is inferior, and is the outlet 

 to a proboscis similar to that of Polyno'e, but armed with less 

 powerful jaws. At the superior base of every foot there is a 

 rounded protuberance which gives origin to a cirrus, and which 

 also carries a scale on such feet as have this appendage, a fact 

 inconsistent with the theory which maintains that the scales 

 are mere modifications of the cirri. On the anterior part of 

 the body the scales appear and disappear on every other seg- 

 ment, but subsequent to the twenty-sixth pair of feet there is 

 one to each segment, and two or more to the two last segments, 

 so that their number is always considerable. The feet are 

 distinctly divided into two branches; the superior branch ter- 

 minated with a single brush of bristles, the inferior sometimes 

 with one and sometimes with two, but the bristles are shorter. 

 The inferior cirrus is very obvious and is inserted far from the 

 extremity of the foot. The appendages of the anal ring form 

 two tentacular styles. As to the branchiae, there is no trace of 

 them at the base of the feet, and when Audouin and Edwards 

 inform us that they seem to be replaced by the fringes which 

 garnish the external margin of the elytra, they surely forget that 

 these fringes are not more developed than they are in Polynoe, 

 and their structure is very unlike that of a respiratory organ. 

 1. S. Boa, scales entirely covering the back, reniform ; an- 

 tennae three, the odd or medial one twice as long as the late- 

 ral ; palpi elongate. Plate XXIII. fig. 6. 



Sigalion Boa, Johnston in Mag. Nat. Hist. vi. 322. fig. 42. 

 Hob. Under stories near low water mark ; not uncommon in Berwick 

 Bay. 



