THE GRADUAL DISPERSION OF Certain Mollusks in New England, By Edward S, Morse. [From the Bulletin of the Essex Institute, Vol. XII.] The gradual dispersion of certain Moll us As in New England. Edward S. Morse. The rapid dispersion of Mollusks, as observed in certain species, is of great interest in connection with the general distribution of species from certain centres. The rapid invasion of large areas, by species not known to have occurred there before, may account for the wide distribution of species through certain geological horizons, where their progenitors in earlier deposits are not known. The sudden appearance of species throughout large geo- logical areas has always been held as a strong point by those who argue against the doctrine of derivation. In a long study of the Mollusca of New England for the past twenty-four years, I have observed many changes going on in the distribution of certain species which in- dicates a much more rapid invasion of areas than had before been supposed. Not only do we see this rapid introduction of forms from other centres, but some species of mollusks vary greatly in their relative scarcity and abundance, when observed over considerable lapses of time. In my little work entitled "Observations on the Terres- trial Pulmonifera of Maine,” forming the first part of the Journal of the Portland Society of Natural History, published in 1864, I commented on this change in the relative scarcity and abundance of certain species as compared with the observations made by Dr. J. W. [From the Bulletin of the Essex Institute. Vol. 12, I860.] 3 4 Mighels, a careful and enthusiastic worker in the same Held. Ilis paper was published in the Proceedings of the Boston Society of Natural History in 1843, and was entitled "Catalogue of the Marine Fluviutilo and Ter- restrial Shells of the State of Maine” (Bost. Jour. Nat. Hist., Vol. IV, p. 808). The following is a britf extract from my paper above mentioned. The lines in quotations being taken from Dr. MighePs paper, while the contrasts as observed by me are printed in italics. Mesodon albolabris. “ Solitary." Great abundance. Anguispira alternata. “ Abundant.” Not abundant, except on inl- ands. Hyalina Indentata. “ Appenrs to be rare.” Not rare. Hyalina electrina. “ Rare.” (Juite common. Conulus chersina is more ubuudant than his words would seem to indicate. Strobila labyrinthica. “ Found sparingly." Common all over the State. Fupillas and Isthmias. Were noted as found sparingly by Dr. Mi- ghels. Most of the species are quite common. Zoogenetes harpa. Is now abundant in several parts of the state, and particularly about Portland. Mighels did not find it at the time of the publication of his catalogue. Succiuea avara. Mighels mentions only one locality. It is now common all over the state. Helisoma bicarinata. “Not aware that it is abundant anywhere.” Exceedingly abundant. Ancylus rivularis. “Found in plenty." One of our scarcest shells. Radix ampla. This species was found in great ubundunce when first discovered in Eagle Lake in the northern part of the state, in company with rhysa ancillaria. In company with Mr. John M. Gould, I visited this lake in 1859, and a most careful search revealed only a few dead specimens of It. ampla, and not a vestige of rhysa ancillaria. Mr. Fuller has since discovered tire shell on the shores of Lake Sebago. Dr. C. B. Adams first described a species of land snail known as Papilla badia, as occurring in Vermont. The shell differed very slightly from a European species P. 5 muscorum, and as such Adams’ species is now recognized, though I have already pointed out some slight differences in the two shells. Since Adams’ discovery of the species, in this country, it has been found on certain islands in the Gulf of St. Lawrence, as well as in New York State. In the year 1862, Mr. Charles B. Fuller found it in Mai ne, near Portland. In some localities near that city, known to have been examined by early collectors without meeting with it, it has been collected by thousands. At Oak island, Chelsea, a famous collecting ground of Dr. Gould, Dr. Binney and others, no evidence of the ex- istence of this species there is recorded. In the year 1860, Prof. W. C. Cleveland found it in the greatest abundance. In this case it can be positively asserted that the species has been introduced within twenty years. The collectors of Salem and Lynn had failed to observe its occurrence in Essex County. Last summer I discovered the species in great abundance on Lowell island in Salem harbor. From these evidences it is quite certain that this minute land shell is being distributed with considerable rapidity. It will be found that, as in the case of plants, the land species of mollusks are being widely distributed through railway traffic. I have often found, at Portland, minute laud shells clinging to firewood that had been brought from the interior of the state. The remarkable rapidity in the diffusion of Littorina litorea is of special interest in this connection. This well-known European species was first observed on this continent by Mr. Willis, of Halifax, N. S., many years ago. Since that time, it has been rapidly and widely dif- fused along the coast of New England. In 1870, Mr. Fuller found a few specimens in Portland harbor, and about the same time at Kennebunk in Maine. 6 It is now found in great abundance along the coast of Maine. Before the year 1872, it had never been observed in Salem harbor. On the shore of South Salem, a place where I had repeatedly collected, only a single specimen was found in the spring of 1872. It is now one of the most common shells in the harbor of Salem, and actually swarms in countless numbers in all the inlets in the vicinity of Salem. Professor Verrill, in a note to Sillinmu's Journal, for September, 1880, records his observations in regard to its diffusion, from which we quote Ihe following: * In 1878, it was collected in abundance at Saco, Me., by the U. S. Fish Commission, and was found sparingly at Peake's island, Casco Bay. In 1872, it was very rare at Provincetown, Mass., but in 1878, it was common there. In 1875, it was collected by the writer at Barn- stable, Mass., on the shores of Cape Cod Bay, in large quantities. In 1871), it had become exceedingly abun- dant at Provincetown. In 1875, our parties found two specimens only on the southern chores of Cape Cod at Wood’s I loll, biit in 1870, it was found to be common there, and is now very abundant. The first specimen, found so far westward as New I l iven, was obtained by Professor S. I. Smith, during the past winter. Other solitary specimens have since been obtained here by Mr. E. A. Andrews and by J. II. Emerton. It is at present exceedingly abundant at Newport, K. I.” In " Science News ” for April 15, 1871), Mr. Arthur F. Gray comments on the occurrence of this species on the New England coast and gives a large number of places where it has been collected. lie first found it in Massachusetts, at Danvers, in the spring of 1872. He also mentions that Prof. J. W. 7 Chickering, jr., found it ;it Hampton beach, X. II., in 1871. The following rude map illustrates the gradual dispersion of this species from Maine southward, with the year of its occurrence marked at the different places. P., Portland, Maine; Pkovn, Provincetown, Mass; W. H., Wood’s Holl. EXPLANATION OF MAP. In 1872, it was observed simultaneously at-Salem, Mass., and Provincetown on the end of Cape Cod. This Cape seemed to form a barrier for some time to its passage south, and after rounding the Cape, its progress was much slower. Its occurrence at Wood’s IIoll being observed in 1875, and only the past year had it got as far as New Haven. A study of the ocean currents north of Cape Cod, which have a southerly course, will account for the rapid dispersal of this mollusk from Maine to Provincetown, Mass. ; while the currents which set easterly south of 8 Cape Cod will account for its slower dispersion along tlx* Connecticut shores. It seems somewhat remarkable that this mollnsk, for so many years an inhabitant of Nova Scotia and the Hay of Chaleur, should have been so long finding its way to the State of Maine. As far back as 18")"), I received speci- mens of this species from Bathurst in the Hay of Chaleur. The conditions are evidently very favorable for its ex- istence along our shores, for it has increased in countless numbers, and the species seems to be fully as robust, and oftentimes exceeding in size its relatives in Europe. Mr. Gray calls attention to the fact that this species, known under the common name of "periwinkle,” forms an abundant supply of food to the poorer classes in Great Britain and Ireland, and there is no reason why the poorer classes here should not avail themselves of a mol- lusk so easily obtained. Believing that, in past times as at present, the dispersion of forms took place in similar ways, it is interesting to look ahead to a time when the present mud and sand of the shores shall have l>een converted and consolidated into stratified rocks with the species entombed in a fossil condition. We may imagine a future Barrande finding material for an onslaught on the derivative theory by pointing to the abundant occurrence of this species in a narrow bed of rock of the same horizon and occurring over hundreds of miles of territory, when tho beds just below reveal no vestige of this large and vigorous spe- cies. I.ittorina litorea, linn.