44 



ESSAY ON CLASSIFICATION. 



sentatives of the other three branches associated, as we 

 find them all four in the sea. Classes have already a 

 more limited range of distribution. Among Radiata, the 

 Polypi, Acalephs and Echinoderms 1 are not only all aqua- 

 tic, but they are all marine, with a single exception, 2 

 the genus Hydra, which inhabits fresh waters. Among 

 Mollusks, 3 the Acephala are all aquatic, but partly ma- 

 rine and partly fluviatile ; the Gasteropoda partly marine, 



1 For the geographical distribu- 

 tion of Radiata, consult : DANA (J. 

 D.), Zoophytes. United States Ex- 

 ploring Expedition, under the com- 

 mand of Ch. Wilkes, U.S.N., Phila- 

 delphia, 1846, 1 vol. 4to.; Atlas, fol. 

 MILNE-EDWARDS et HAIME (JuL.), 

 Recherches sur les Polypiers, Ann. 

 Sc. Nat. 3e ser., vol. 9-18, Paris, 1848- 

 52,8vo. ESCHSCHOLTZ (Fn.), System 

 der Acalephen ; Berlin, 1829, 4to., 

 fig. LESSON (R. PR.), Histoire natu- 

 relle des Zoophytes, Acalephes; Paris, 

 1 843, 1 vol. 8vo., fig. KOLLIKER (A.), 

 Die Schwimmpolypen und Siphono- 

 phoren von Messina; Leipzic, 1853, 

 1 vol. fol., fig. LEUCKART (R.), Zoo 

 logische Untersuchungen ; Giessen, 

 1853, 4to.; Zur nahern Kenntniss der 

 Siphonophoren von Nissa, Arch. f. 

 Naturg., 1854; Beitriige zur Kennt- 

 niss der Meduseufaune von Nissa, 

 Arch. f. Naturg., 1856. GEGENBAUER 

 (C.), Beitriige zur nahern Kenntniss 

 der Schwimmpolypen, Zeitsch. f. wiss. 

 Zool., 1853; Versuch eiues Systems 

 derMedusen,mit Beschreibung neuer 

 oder wenigbekannterformen, Zeitsch. 

 f. wiss. Zool., 1856. VOGT (C.), Re- 

 cherches sur les animaux inferieurs 

 de la Mediterranee; Genfeve, 1854. 

 MULLER (J.) und TROSCHEL (F. H.), 

 System der Asterideu, Braunschweig, 

 1842, 8vo., fig. AGASSIZ (L.), Cata- 

 logue raisonne des families, des genres 

 et des especes de la Classe des Echi- 

 nodermes, Ann. des Sc. Nat., 3e ser., 

 vol. 6-8; Paris, 1847, 8vo. 



2 I need hardly say in this con- 

 nection that the so-called fresh- 



water Polyps, Alcyonella. Plumatel- 

 la, etc., are Bryozoa, and not true 

 Polyps. 



3 For the geographical distribution 

 of Mollusks consult : LAMARCK ( J. 

 B. DE), Histoire naturelle des Ani- 

 maux sans vertebres, Paris, 1815-22, 

 7 vols. 8vo.; 2de edit, augmentee de 

 notes par MM. DES!IAYES et MILNE- 

 EDWARDS, Paris, 1835-43, 10 vols. 

 8vo. FERUSSAC (J. B. L. DE), His- 

 toire naturelle des Mollusques terres- 

 tres et fluviatiles; Paris, 1819, et stiiv, 

 4to., fig., fol., continuee par DES- 

 HAYES. FRUSSAC (J. B. L. DE) et 

 SAN DER- RANG (A.), Histoire naturelle 

 des Aplysiens; Paris, 1828, 4to., fig., 

 fol. FERUSSAC (J. B. L. DE) et D'OR- 

 BIGNY (A.), Monographie des Cepha- 

 lopodes cry ptodibranches ; Paris, 1 834- 

 43, fol. MARTINI (F. H. W.) und 

 CIIEMNITZ (J. H.), Neues systema- 

 tisches Conchylien-Kabinet ; Niirn- 

 berg, 1769-95, 11 vols. 4to., fig.; new 

 edit, and continuation by SCHUBERT 

 and A. WAGNER, completed by H. C. 

 KUSTER, Niiruberg, ] 1 vols. 4to., fig. 

 KIENER (L. C.), Species general et 

 Icouographie des Coquilles vivantes ; 

 Paris, 1834, et suiv, 8vo., fig. REEVE 

 (LOVELL), Conchologia Iconica ; a 

 complete Repertory of Species of 

 Shells,Pictorial and Descriptive ; Lon- 

 don, 1843, and foil., 4to., fig. PFEIF- 

 FER (L ), Monographia Heliceorum 

 viventium; Leipzig, 1847-48, 8vo. 

 PFEIFFER (L.), Monographia Pneu- 

 monopomorum viventium ; Cassel, 

 1852, 8vo., and all the special works 

 on Conchology. 



