The sea-whips and sea-feathers are varieties of gorgonias, which are named from their forms. Some have shapes which resemble branching shrubs; others are long unbranched rods, either straight or spiral. They attain a height of several feet and are of various colors. The colony has a horny axis surrounded by a living mass which resembles a sheet of animal matter. This mass consists of polyps closely united, and has throughout its substance spicules of carbonate of lime, making it a kind of calcareous crust or bark. In dried specimens this becomes very brittle, and is easily broken from the horny axis. (Plates XLVI, XLVII.) [Illustration: PLATE XLVI. GORGONIAS. Eugorgia aurantica. Muricea specifera. Pterogorgia acerosa. Gorgonia anceps.] [Illustration: PLATE XLVII. Leptogorgia rigida (a gorgonia). Eunicea lugubris (a gorgonia). Gorgonia flabellum (a gorgonia). Leptogorgia Agassizii (a gorgonia). Pennatula borealis and P. aculeata (sea-pens).] The sea-fans are colonies with a central, horny, flexible, and much-branched axis, covered, as in the sea-whips, with a layer of united polyps containing spicules of lime, which make a somewhat [pg153] firm crust. This, in dried specimens, breaks off readily. The colony branches profusely, or rather separates by fission, in one plane, the large and small branches making a network of fan-like shape and often of great fineness and intricacy. These fans attain a length of several feet and a corresponding breadth, and are abundant in semi-tropical as well as in more southern waters. In color they are red, yellow, brown, or purple. ORDER =PENNATULACEA= SEA-PENS These singular colonies resemble quill-feathers, such as are used for pens, and are named for this reason. The long, horny central axis is naked below, and is partly buried in the sand, but is not permanently attached. The upper portion of the axis has two rows of short, opposite, lateral branches; on the upper side of the branches the polyps live in separate inclosures. Spicules of lime are present in the substance of the branches, which gives them stability. Sea-pens are found at moderate depths and are widely distributed. They are highly colored and phosphorescent. [pg154] TABLE SHOWING THE CLASSIFICATION OF THE CTENOPHORA DESCRIBED IN THIS CHAPTER Class =CTENOPHORA= Order =CYDIPPIDA= (/Two tentacles, retractile into sheaths/) Genera Species ^Pleurobrachia^ ^P. rhododactyla^ Order =LOBATA= (/Numerous lateral tentacles contained in a groove; body compressed; two large oral lobes/) ^Bolina^ ^B. alata^ ^B. septentrionalis^ ^B. vitrea^ ^Mnemiopsis^ ^M. Leidyii^ Order =CESTIDA= (/Ribbon-like form, from body being extremely compressed in the vertical plane/) ^Cestum^ ^C. veneris^ Order =BEROÏDA= (/No tentacles; mouth very wide; gullet occupies greater part of body/)