426 Dr. Johnston on the British AphroditacecB. 



garnished Avith scales which alternate with other feet desti- 

 tute of that appendage is unquestionably one of the most im- 

 portant characters of the present family and its leading pecu- 

 liarity. 



The elytra are very variable in number, and their shape is 

 not always alike. From their structure it appears probable 

 that they are subservient to respiration, yet we see them often 

 associated with organs to which the name of branchiae has 

 been given. These are concealed below the elytra, and have 

 the form of small crests or cutaneous nipples ; they occupy the 

 upper part of the base of the feet and are always placed within 

 and above the cirrus of the dorsal branch. Sometimes these 

 little appendages are scarcely visible, and they are very rarely 

 to be detected on the squamigerous feet, — that is, on the feet 

 of the second, the fourth, the fifth, the seventh, the ninth 

 segments, and so on. This binary alternation of branchial 

 with abranchial feet is to be observed even in the species 

 which have no elytra [Palmyre) ; but it is not so constant as 

 has hitherto been believed, for in the genus Acoete branchial 

 tubercles exist on all the feet, their number being only fewer 

 on the segments which carry the elytra. 



In the families alUed to AphroditaceaB there are species 

 which present no visible branchiae, but when these organs 

 exist, their form or their position is essentially different. Thus 

 in the Nereides they affect the form of little fleshy tongue-like 

 processes placed at the end of the foot between the superior 

 and inferior cirrus ; and although in the Euniceacees and the 

 Amphinomenacea they have nearly the same position as in the 

 Aphroditace^e, their configuration is very dissimilar ; being in 

 the form of filaments more or less pectinated, of tufts, of ar- 

 buscules, or of pinnatifid leaflets. 



In the majority of Aphroditaceee the presence of elytra 

 coincides with the absence of superior cirri, that is, we find 

 the latter only on such feet as carry branchiae and do not bear 

 scales. But this character, like the preceding, is liable to ex- 

 ception, for in Siffalion there is a superior cirrus to every seg- 

 ment of the body whether elytrous or not, and this fact ap- 

 pears to invalidate the opinion of those who maintain, with 

 Blainville, that the cirri are the analogues of the elytra, or mo- 



