NOKTHWEST COAST MARINE SHELLBEARING MOLLUSKS. 3 
of opinion are to be expected. The International rules of nomencla-» 
tore have been rigidly followed, in the belief that the progress of 
science depends largely on standardization of names, however pain- 
ful it is to note the disappearance of familiar but erroneous designa- 
tions. The accuracy called for by the present state of the science 
should not be relaxed to satisfy the protests of amateurs in taxonomy. 
In compiling this list I have taken advantage of the work of my 
colleague, Dr. Paul Bartsch, who has with great care and intense 
microscopical study worked out the species of minute forms, such as 
the Pyramidellidae, Rissoidae, Synceratidae, and Caecidae, and have 
adopted his results as published in the Proceedings of the United 
States National Museum during the last few years, with only such 
changes as the jjrogress of science since their publication has made 
advisable. Many forms which on a superficial examination by the 
older authors were regarded as mere mutations of a single species 
have proved on microscopic study to possess constant characters fully 
entitling them to specific rank. In general, whenever the characters 
seem to justify it, I have preferred to record separately forms vv^hich, 
on the examination of only a few specimens, might have been 
regarded as mere mutations. By thus separating them, often from 
examination of a multitude of individuals, attention is called to their 
characters, and future students will have an opportunity to exercise 
their judgment on the question of specific distinction when otherwise 
it might have been entirely overlooked. 
Many of the species with a wide geographical range follow the 
isotherms, and when collected in the north appear to be denizens of 
moderate depths, but in the southern part of their range are found 
only at great depths where the temperature of the water is the same 
as in their more boreal habitat. It becomes difficult therefore to de- 
termine which species are really members of the archibenthal fauna. 
I have in the following discussion regarded only those found exclu- 
sively in depths of over 200 fathoms as belonging to that fauna, and 
therefore the number of species of that group in the table ma}^ seem 
unduly small, for many of the others also reach great depths in part 
of their range. 
A veiy few exceptional cases occur where species are known from 
deep v/ater in the northern part of their range yet have been obtained 
in moderate depths in the south. Transportation and regurgitation 
by fishes may account for this anomaly which must await more 
thorough collection of living specimens for explanation. 
In certain cases of anomalous distribution reported by collectors, 
and when I have not examined personally authentic specimens, I have 
appended the name of the authority for the locality. A former habit 
of the Spanish women of southern California, of preparing shell 
work for sale to tourists and of carrying their baskets of shells (often 
