NO. 2565  POLYCHAETA AND AMPHIPODA—REISH AND BARNARD 13 
their populations in the open sea at these latitudes, include Oorophium 
uenoi, Allorchestes angustus, Hlasmopus rapaz (sensu stricto), Ampithoe 
valida, Pontogeneia minuta, and Ampithoe longimana. These are pri- 
marily confined to the innermost reaches of the bay, in or near marsh- 
land channels. Generally, they are also among the most abundant 
species of any of the samples, as the following ranked list of species 
and numbers of individuals in 26 samples shows: Corophium uenoi 
(1131), Aoroides columbiae (808), Corophium spinicorne (333), Ampi- 
thoe lacertosa (242), Microdeutopus schmitti (205), Pontogeneia rostrata 
(194), Corophium acherusicum (187), Allorchestes angustus (116). 
Note, however, that Hlasmopus rapaz, Ampithoe valida, Pontogeneia 
minuta, and Ampithoe longimana are rare in these samples. The dis- 
continuity of many of the typical open-sea species from the sea to the 
inner reaches of Morro Bay is probably due to the unsuitable, coarse, 
sandy substrates, rapid tidal currents and lack of benthic algae at 
the seaward stations. 
Species and genera known to occur in Bahia de San Quintin (table 
2) that were not discovered in Morro Bay and that are considered to 
be absent because of geographic thermal differences are: Acwmino- 
deutopus, Rudilemboides, Lembos macromanus, Amphideutopus, Orcho- 
mene magdalenensis, and Pontogeneia quinsana. 
Other San Quintin species that, in the open sea, extend to the north 
of Morro Bay and probably are excluded from the estuary for reasons 
other than thermal structure are Ampelisca compressa and Hyale 
frequens. The absence of both species is striking and unexplainable. 
The most unusual difference between Bahia de San Quintin and 
Morro Bay is in the species of Ampelisca that dominate the benthos; 
in San Quintin Ampelisca compressa is the dominant; this species 
occurs northward in the open sea to Puget Sound, Washington, but 
in Morro Bay (and in Tomales Bay, material at hand), the principal 
species is A. cristata. Both A. compressa and A. cristata, however, 
are known to occur in tropical Pacific and tropical Atlantic America, 
so that neither can be considered a warm or a cool-sea species. Other 
species of Ampelisca occur only incidentally in Newport Bay. 
Although the plant is widespread in Morro Bay, stands of the eel- 
grass, Zostera marina, do not seem as dense in Morro Bay as in Bahia 
de San Quintin. That eel-grass is not so prominent in Morro Bay as 
in San Quintin is shown by the absence or low rank of Hyale, Ponto- 
geneia, and Ericthonius, genera of amphipods which characterize the 
San Quintin eel-grass beds (Barnard, 1964). On the other hand, a 
relatively higher incidence of algae is indicated in Morro Bay by the 
high rankings of Corophium, Aoroides, and Ampithoe. 
The influence of the dense populations associated with pilings in 
Newport Bay is now confirmed in comparing the fauna of that bay 
