288 TORREY. 



The lophophore organ is extremely variable and may be 

 present or absent, as in P. psammophila. It may resemble 

 that of P. australis, though differing somewhat in shape 

 (Fig. 5). In this case it is simple, with a thickened glandular 

 epithelium lying for the most part against the inner circle 

 of tentacles, and an outer free non-glandular edge of much 

 lower cells. In another case, however, it had the form of the 

 same organ in P. arcJiitecta and P. psammophila, as described 

 and figured by Andrews and Cori, being composed of a basal 

 lobe and a distal "carpel-like organ." This condition seems 

 to have been attained by the addition of the "carpel-like organ" 

 to the structure (basal lobe) which corresponds to the entire 

 organ in P. australis. 



The following is a diagnosis of the species, from material 

 preserved in alcohol and formalin : 



Total length may be 9 cm., of which the tentacles represent from 2^ to 



4 mm. 



Diameter, i \ to 2 mm. 

 Lophophore spirally coiled, each spiral possessing from ii to 2 complete 



turns. 



Tentacles 170 to 200. 



Lophophore organ present or absent ; extremely variable in form. 

 Each animal occurs singly and completely fills tube. 

 Tube straight, cylindrical, composed of delicate chitin, encrusted with fine 



sand grains. 

 Ridge of thickened epithelium in the descending limb of the digestive canal, 



just beneath the median longitudinal blood vessel. 

 Longitudinal nerve trunks unite across median line between mouth and 



anus. 

 Longitudinal muscles in numerous very high and narrow folds which reach 



their maximum in the distal third of the body. 

 Sexes possibly separate. 



Localities: Puget Sound, Washington; Humboldt Bay, California, on sand 

 and mud fiats that may be uncovered by the tide. 



COLUMBIA UNIVERSITY, January, 1901. 



