The common European sea-mouse (
Aphrodita aculeata) has been so frequently and so widely reported from the American Atlantic coast, while none of the writers on our annelids have reported any other species, that the identity of the species occurring on the two sides of the Atlantic has been taken as established. It was, therefore, with genuine surprise that I found, while preparing a description from Wood's Hole specimens for a report on the annelids of that region, certain obvious points of difference between these and
A. aculeata as described by European writers. Since returning to Philadelphia a more thorough examination of the literature and a detailed comparison of specimens in the collection of this Academy with those belonging to the U. S. F. C. laboratory at Wood's Hole, kindly sent to me by Mr. Vinal Edwards, and two specimens of
A. aculeata from the neighborhood of Helgoland, for the opportunity of studying which I am indebted to Dr. W. McM. Woodworth, of the Museum of Comparative Zoology, have doubly convinced me of the wide distinction between the species common in the deeper waters of the open sea off the Wood's Hole region and the European species. This does not, of course, exclude the possibility of the occurrence of the true
A. aculeata also on our coast, yet the few notes furnished by Prof. Verrill in his Report on the Invertebrates of Vineyard Sound lead to the belief that the species therein recorded as
A. aculeata is the one herein described, which it seems probable is the only one occurring south of Cape Cod.
