THE NAUTILUS. 99 
naturalists, which have come under my notice have all appeared to 
me to be referable to C. fornicata (1) Lam., or to the variety of 
C. convexa Say which has grown upon a broad, not very convex, or 
perhaps a partly concave surface. A fine series of shells from Cape 
May, submitted to me by Mr. Ford as C. glauca come under the 
latter category. They are distinct from C. fornicata, but they do 
not show the characters called for by Say’s description, which in 
itself presents no features to distinguish the shell he describes from 
the young and spotted form of C. fornicata, to which I have no 
doubt it belonged. Such shells are in the National Museum labeled 
C. glauca by Stimpson. It may not be-known to all our concholo- 
gists that the extremely high and usually dark-colored forms of 
Crepidula, such as C. convexa (typical) and C. adunca of California, 
derive their peculiar appearance from roosting on some gasteropod, 
and that wider and less elevated forms of the same species can 
almost always be found, if not in the same locality, at least in a 
geographical series of wide range. The difficulties, in the way of a 
satisfactory determination of such semi-parasitic forms as the Calyp- 
treide are very great, and increase in my experience with the 
amount of material subjected to study. That there may be a distinct 
form entitled to be called C. glauca I do not wish positively to deny, 
but I must confess that I have never seen one and therefore have 
grave doubts of its existence. 
A LIST OF THE MOLLUSCA OF COLORADO. 
(Compiled for the Colorado Biological Association.) 
BY T. D. A. COCKERELL. 
In the “ Journal of Conchology,” vol. vi, pp. 60-65, I gave some 
bragn ao ye _ a 
preliminary remarks on the Mollusea of Colorado, stating that from 
the lack of records and other reasons, a complete list could not then 
be prepared. Since then a considerable amount of material and 
information has been gathered, and while much remains unknown, 
there is sufficient ascertained to seem to warrant the presentation of 
a faunal list. In this list the localities are not all given in detail, as 
