Zool.-Vol. I.] JOHNSON— PACIFIC COAST ANNELIDS. 175 



ticulata, and most, if not all, species having 18 pairs. 

 Between the thirty-third and forty-ninth somites, the elytro- 

 phorous and cirriferous somites alternate regularly. On 

 somites 49 and 50 elytra are borne. From this point onward 

 the arrangement differs in different individuals, but long 

 series of elytrophorous somites are the rule, alternating with 

 pairs and trios of cirriferous somites. In one example the 

 groups of elytrophorous somites run as follows 1 : 



Three Somites 56-5S 



Five " 61-65 



Eight : . . . . " 68-75 



In every instance I have found two long series of elytra- 

 bearing somites at the posterior end; and it is in one or the 

 other of these series that the extra elytron is found. 



The replacement of an elytron by a dorsal cirrus on the 

 opposite side of one and the same somite is no argument for 

 the homology of these organs, as might at first seem to be 

 the case. It is obvious that the mere absence of the elytron 

 may be the determining factor leading to the development 

 of the dorsal cirrus. 



Polynoe lordi {Baird). 

 Plate VII, Figs. 35, 44; Plate VIII, Figs. 51, 51a, 516. 



Lepidonotus lordi Baird. Proc. Zool. Soc. (London), April, 1863, 



p. 107. 

 Halosydna lordi Baird. Jour. Linn. Soc. (London), Vol. VIII, 



1865, p. 190. 



Body long and tapering gradually to the attenuated posterior extremity, 

 thickest in anterior third from eighth to twentieth somite, slightly diminish- 

 ing towards the head. 



Prostomium (fig. 35) broader than long, bilobed, widest across posterior 

 portion at level of anterior pair of eyes. Eyes four, of about equal size, pos- 

 terior pair at extreme base of prostomium, nearer together than the anterior. 

 Antenna? with joint at base, inserted slightly below level of basal joint of ten- 

 tacle. Antennae and tentacle short and stumpy, but with long filiform tips; 

 slightly longer than prostomium. 



Peristomial and dorsal cirri (fig. 51) short, fleshy, club-shaped, with long 



1 This specimen has 45 elytra on the right side, 44 on the left. The extra elytron of the 

 right side occurs on somite 69. The enumeration above given is for the right side. 



