66 THE NAUTILUS. 
lique parallelogram; others, from Michigan and Minnesota, are 
very high, the altitude equalling or even exceeding the length. 
Some of these Jocal forms may prove to be true varieties. 
This Pisidium has caused considerable trouble, correspondence 
and controversy for a long time. Almost two years ago it was 
recognized as a well-defined species, and given its present name. 
Then Mr. E. W. Roper obtained a type specimen of Pis. ferrugi- 
neum Prime, from the Museum of the Boston Society of Natural 
History, which he kindly sent me for comparison, and we were both 
satisfied at once that it was identical with the present species. 
Several examples, of T. Prime's own hand, also named P. ferrugi- 
neum, from “ New York,” in my collection, probably none of them 
mature, are of the same species. After this, the present name was 
suppressed, although it was evident that all these Pisidia were very 
far from being congruent, as to size and shape, with the author’s de- 
scription and figures of Pis. ferrugineum, in Mon. Pis. and Mon. 
Corbiculadae. Among the thousands of specimens seen from New 
England and New York, none could be referred to these descrip- 
tions, and so necessarily the question arose: What, and where, is the 
true P. ferrugineum of Prime’ Last winter, Mr. Roper received sey- 
eral lots of Pisidia from Cambridge and Waltham, Mass., and from 
Maine, and obliged me by forwarding them for examination. 
Among them there was undoubtedly the long sought for Pis. ferru- 
gineum, in every particular conforming with the author’s description 
as well as the figures in Mon. Pis. (Pl. XII, figs. 8, 9,10). Nowwe 
knew also that Pis. paupereulum was distinct and deserving a name 
of its own. The mixing up of the two species by Prime, is ex- 
plained by the fact that both of them are usually covered with a 
dark or blackish “ ferruginous ” substance, in the same way, giving 
them the same outward appearance, the more so as in some forms or 
specimens of Pis. pauperculum the beaks are rather high and promi- 
nent, though rounded, and not “tubercular,” without ridges (Conf. 
the figures cited above). Under the impression that they were iden- 
tical, the author could say that P. ferruginewm was one of our most 
common species, while properly restricted, it seems to be rather rare. 
Pisidium scutellatum n. sp. 
Mussel of medium size, rather high, oblique, markedly protracted 
downward in its anterior part, well rounded, rather strongly in- 
1 The author himself could not be consulted, since he had given up, long 
ago, the study of these mussels. 
g0, uf 
