114 THE NAUTILUS. 



The clam is Tapes staminea Conrad, and while this was the most 

 abundant species, other bivalves, as Gardium nuttalli, Cunrad, and 

 some species of Macoma were present in fair numbers. It was 

 however only on the Tapes that any Isapis were found. On these 

 they adhered quite closely, so that the digging, and even a rinse 

 did not appear to dislodge them. 



While it was seldom that I found more than two or three Isapis 

 on one shell, and usually only one, in several cases, I took a Tapes 

 with a whole lot of small fry massed together, perhaps as many as 

 20 fine shells, and others had what looked like the spawn. Thei^" 

 position on the Tapes was always close to the lips, and I think nearly 

 always in the depression close to the beaks. Besides this species I 

 took more rarely on the Tapes, a species of Odostomia (Ivalea); it 

 also occurred on the Gardium. Dr. Bartsch says of it, " too young 

 to permit of positive specific identification." This Ivalea may have 

 been more abundant than I found it, being of such small size, and as 

 I discovered very easily rubbed off. It appears to me not unlikely 

 that Isapis fenestrata, may have similar habits, and that therefore, 

 where it has been taken dead and rarely, it may prove quite as 

 plentiful as 1. ohtusa has in this case, I should say that in our 

 Northern waters, ohtusa must be very local, or it would surely have 

 been turned up " dead " long before this, by the collectors, who 

 have done considerable collecting and dredging on our British . 

 Columbia coasts. 



Included in this sending to Dr. Bartsch was Odostomia (Amaura') 

 talpa Dall & Bartsch, which appears to be new to our B. C. Lists, 

 and which species I gathered in (air numbers in this same spot, at 

 extreme low tide, all dead and containing hermit crabs. 



THE ANATOMICAL STRTJCTURE OF CERTAIN EXOTIC NAIADES COM- 

 PARED WITH THAT OF THE NORTH AMERICAN FORMS. 



BY DR. A. E. ORTMANN. 



{Continued from p. 108.) 



Gills long and narrow, the inner the wider. Edge of inner gill 



with the usual longitudinal furrow, which is missing on the outer 



gill. Outer gill gradually narrowing anteriorly, its anterior end 



situated at the highest point of the mantle-attachment line. Inner 



