Mr. J. D. Dana on some genera of Cyclopacea. 181 XXIII. Notice of some Genera of Cyclopacea. By J. D. Dana. As a preface to the descriptions which follow, a classification of Crustacea is here given ; it is made out so as to exhibit to some extent the parallel relations of the several orders and subdivi-sions. CRUSTACEA. Subclassis I. PODOPHTHALMIA Ordo l« Decapod a. Tribus 1. Brachyura. 2. Anomoura. 3. Macroura. Ordo 2. Schizopoda. Tribus 1. Stomapoda. 2. Diploopoda. Subclassis II. EDRIOPHTHALMIA. Ordo 1. Choeistopoda*. Tribus 1. Isopoda. 2. Lsemipoda. 3. Amphipoda. Ordo 2. Entomosteaca. Subord. 1. GNATHOSTOM ATA f Tribus 1. Branchipodacea. 2. Limnadiacea. 3. Daphniacea. 4. Cyclopacea. 5. Cypridacea. Subord. 2. COEMOSTOMATA J, Tribus 1. Caligacea. 2. Lernaeacea. 3. Nymphonacea. Subord. 3, Meeostomata §, Tribus 1. Limulacea. Ordo 3. Teilobita. Subclassis III. MANDYATA | Tribus 1. Cirripeda, or Balanaceaf. Order ENTOMOSTRACA. Tribe Cyclopacea. To avoid explanations in the following descriptions, we here enumerate the prominent external characters of this tribe. Body jointed, the carapax not prolonged beyond the joint to which it belongs ; abdomen not innexed. * From xapio-Tos, separate, and novs,foot, alluding to the fact that the pairs of feet belong each to a distinct segment of the body. f From yvaOos, jaw, and orofia, mouth, alluding to the mouth being fur-nished with proper mandibles and maxillae. I From Kopfios, trunk, and aropa, mouth, the mouth having the form of a moveable trunk § From firjpos, thigh, and oro/ia, mouth, the basal joints of the legs con-stituting the jaws. || From navdvt), a cloak, alluding to the covering in which the body of the animal is inclosed. Tf The Cypris-like young of several Anatifce were collected and figured by the writer, and the metamorphosis traced to the adult state. When first found swimming free in the ocean, they were taken for a new genus allied to Cypris, so similar are their forms. The fact that the body and legs of the Cirripeda shed their skin, is further evidence of the propriety of placing this group with Crustacea. The pedicel of the Anatifce corresponds to a pair of antenna? in the young; the animal attaches itself by the sucker-like disc terminating these organs before the metamorphosis commences, and in a group of Anatifce all the dif-ferent stages may be observed, from the pair of distinct antenna? to the fixed simple pedicel.