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others, are absolutely and positively harmless, few, if any, being able even to scratch by their bite enough to tear the skin.
Ichthyology.—The fishes of the District present but few peculiarities; almost all of the species belong to genera that are represented in the northern as well as the southern States, species characteristic of the two sections of the country being here intermingled. Representatives of three and perhaps four of the sub-classes into which fishes may be divided are found.
Of the true fishes, or Teleostei, there are numerous species which represent many genera.
Some saltwater, estuary, and migratory species ascend as far up as the Falls of the Potomac. The “rock-fish,” or “striped bass” (Roccus lineatus, Gill), and the “white perch” (Morone Americana, Gill), are the best known and the most common. Both of them, but more especially the rock-fish, are much angled for. The white perch is caught principally in the Spring months, and the rock-fish in the Summer.
The “sunfishes” (Lepomis or Pomotis) are also quite numerous in the streams of the District.
Of the Etheostomoids, a family peculiar to North America, representatives have been described, by Dr. Girard, of several generic groups. These are Arlina effulgens, Estrella atro-maculata of Girard, the Percina nebulosa of Haldeman, and perhaps the Hadropterus maculatus of Girard. All of them are small fishes with two dorsal fins, the first of which is supported by slender spines. They appear to represent in the fresh waters of the United States the Gobioids of the Old World, and to be nearly allied to them.
The "bill-fish" (Belone truncata of Lesueur), which belongs to the family of Scomberesocoids, is occasionally caught below the Falls. It is readily distinguished by its snipe-like bill, the dorsal and anal fins placed opposite each other and far back, and by the small scales.
The family of Cyprinodonts is represented by several species confounded under the names of " minnows” and “killie-fish.” They are distinguished by their depressed head covered with large scales, and the posterior position of their small dorsal fin. All of them are of small size.
The family of the true Cyprinoids, as now restricted, has many species, belonging to a number of different gen
The Rhinichthys is a small fish, with a prominent snout, and a blackish band along the side. Two species, belonging respectively to the genera Cyprinella and Clinostomus of Dr. Girard, are among the most interesting, as they are the most eastern representatives of those genera known. They are favorite ornaments of fresh-water aquaria. The common “shiner” belongs to this family, and is the Luxilus chrysoleucas of naturalists.
The“ suckers” belong to a family very nearly allied to the preceding. Two species are quite abundant in the streams of the District. One is a Catastomus, and has a lateral line, or perforated row of scales along the sides, and the other, destitute of such a line, belongs to the genus Moxostoma.
The above-named species belong to one order to which the name of Teleocephali has been given; the Cyprinoids and Catastomoids form a sub-order called Eventognathi ; the Cyprinodonts belong to the Physostomi; and the remainder to the sub-order of Physoclysti.
Of the “cat-fishes" (Nematognathi), there are several species belonging to the genera Amiurus or Pimelodus of many naturalists, and Noturus. The latter is called “stone cat.” The wound inflicted by its spines becomes excessively painful, and has even been known to produce death.
Of the sub-class of Ganoids, the “garpike” (Lepidosteus) and “sturgeon” (Accipenser) are abundant near Washington. They belong to two different orders. The former is easily distinguished by its rhombic enameled scales.
A species of shark occasionally ascends the Potomac River. We then have a representative of the sub-class of Elasmobranchii, and of the order of Plagiostomes.
The lamprey (Petromyzon), belonging to the sub-class of Dermopteri and order of Marsipobranchii, is said to be also an inhabitant of the District.
Entomology.-- The District has its entomological fauna in common with Maryland and northern Virginia, both of which belong to what is commonly called by entomologists the region of the Middle States. Those species only of this region which are peculiar to mountains or to the seashore are naturally wanting in the District. It may be said in general that the soil of the District is not favorable to insect life, as it consists chiefly of clay, sand, and boulders, and becomes too hard and dry in Summer. During the hot season, the insects do not find moisture enough to sustain their existence, and the hardness of the soil prevents them from seeking shelter under ground. The con-. sequence is, that although the number of species occurring here is considerable, the number of specimens is not in proportion. A few more favored localities form an ex
ception to this rule; a walk along Rock Creek and Piney Branch, towards the slashes, where the latter takes its origin, may reward the collector for his exertions. The same may be said of some localities beyond the Eastern Branch, in the valleys between the hills on that side of the river.
Conchology, etc.—The conchology of the District is interesting, the number (86) of shells in its fauna being large for so small a tract of country, which is in consequence of the great variety of stations. Fresh-water shells are particularly numerous, since we have not only a large river with all kinds of shore, muddy below, and rocky above Georgetown; but many smaller streams of all sizes, affording stations for a great variety of species. There are 50 species of fresh-water shells, 18 bivalves (of the genera Cyclas, Pisidium, Unio, Alasmodon, and Anodon), and 32 univalves (Ancylus, Lymnea, Physa, Planorbis, Melania, Anculosa, Paludina, Amnicola, and Valvata). The Unios are best obtained in the still waters of the canal, at the annual drawing-off of the water. The Anculosae and Paludinae are very pretty shells, and are best found at low-water mark on rocks at the Little Falls.
The land shells are of a northern rather than a southern type. There are 20 Helices, of which H. chersina, concava, fraterna, gularis, hirsuta, alternata, lineata, suppressa, tridentata, and thyroidus are the most common. H. thyroidus is sometimes found in gardens; all the rest live in the woods. There are also 4 Succineæ, 1 Bulimus, 6 Pupae, 2 Vertiginae, and 1 Carychium. There is also a Limax and a Philomycus. The Limax comes out in the frosty weather of Novemher, from among the grass
in the Smithsonian grounds, and may be seen upon
the gravel walks in great numbers on sunny mornings.
Of Crustacea, there are two species of cray-fish (Cambarus), C. fossor and C. Pealei ;—the former makes the curious mud chimneys seen in swampy places, the latter lives in the deep water of the river. In small streams there is an Asellus, and a Gammarus. In wells there is found a curious little subterranean shrimp, (Niphargus ?) the first ever found in America, of a genus which has excited much attention in Europe. Pill-bugs (Armadillo, Porcellio, etc.) are very abundant.
Dr. Girard discovered several fresh-water Planariæ in the District, of which the Dugesia Foremanni is one.
The flora of any particular district is controlled to so great an extent by the character of the rocks and soils upon which the plants are found growing, that at the risk of repetition we must state that in the vicinity of Washington the rocks may be divided into two kinds, one lying above the points reached by the head of tide-water in the Potomac and its branches, the other embracing all the country lying south of that line and near the river. The rocks of the first division are mostly gneissoid and slate rocks, the latter consisting of micaceous and talcose slates. Into these have intruded great masses of green stone, forming the heights of Georgetown, and which may be seen in section on the canal, near Georgetown College. It may be mentioned, with regard to these rocks, that Prof. Hitchcock, when on a visit a ew years since to the Great Falls of the Potomac, recognized there the same formation of old slate rocks which in the southern States