272 THE AMERICAN MONTHLY [Oct 



then, Charles, Stodder, residing in Boston, sent me to ex- 

 amine certain slides of Bacillaria from the Bailey cabinet. 

 Among them was one from Halifax, Nova Scotia, contain- 

 ing Hyalodiscus subtilis, the type slide from which had 

 been described the form in question. Then I had in ray pos- 

 session the original from which J. E. G-avit had engraved 

 the celebrated picture, which Mr. Gavit told me was an 

 etching on steel, in the Smithsonian contributions to Sci- 

 ence. It showed at that time just the same as the pic- 

 ture exhibits it. For remember, then one had not immer- 

 sion lenses to work with, and the making of lenses, if we 

 except those of Charles Spencer and some of Tolles, was 

 crude and I may say imperfect. The markings were re- 

 solved with difficulty into two fine lines looking, as Bailey 

 said, like the engine turning on the back of a watch, no 

 more. The centre was always occupied by a rough part, 

 and that was indefinite in outline, with no seeming mark- 

 ings, as they are called, arranged symetrically. There- 

 after I had slides labelled Hyalodiscus subtilis from va- 

 rious sources, but Halifax was supposed to be the true lo- 

 cality. 



In January of 1877, I went to California, partially to 

 study the Bacillaria of the Pacific coast, and I had Hy- 

 alodiscus subtilis or californicus growing in San Fran- 

 cisco harbor w T here I resided along with Arachnoidiscus 

 ehrenbergii. I collected it and had a chance to study it 

 pretty thoroughly. I had it from all along the coast of 

 California. I had it also from the state of Washington, 

 where it is common. I also collected it at Saucellito, just 

 opposite San Francisco on the northern side of the G-olden 

 Grate, a form which proved to be Hyalodiscus cervinus of T. 

 Brightwell and thought it was different from Hyalodis- 

 eus subtilis, J. W. B. for the markings are coarse, being 

 readily resolvable with a f of an inch. The centre is not 

 commonly marked like Hyalodiscus subtilis but the dots 

 are all over the valve and look plainly hexagonal in shape 



