w 



SUBCLASS II 



HYDROZOA— ACALEPHAE 



133 



probably attached to seaweeds, as often in modern hydroids, others were free- 

 floating or planktonic creatnres. 



Remains of Graptolites are profusely distributed in the siliceous schists 

 and alum slates of the Fichtelgebirge, Thuringia, Saxony and Bohemia. 

 They are plentiful also in the Harz, in Poland, Silesia, the Baltic Provinces 

 and the Ural district ; and again in Scandinavia, Cumberland, Wales, the 

 north of England, Scotland and Ireland, as well as in Normandy, Brittany, 

 Spain, Portugal, Sardinia and Carinthia. In America they are found ex- 



a ' h c quisitely preserved in Newfoundland, 



Canada, New York, Virginia, Alabama, 

 Ohio, Wisconsin, Iowa and Arkansas. They 



Fig. 210. 



a, Monograptus nilssoni Barr. Silurian (Alum 

 Schists) ; Gräfenwerth, near Schleitz, Germany; 

 h, Monograptus colonus Barr. Silurian ; Eliots- 

 tieid, Scotland, showing sicula (after Lap- 

 worth) ; c, Monograptus turriculatus Barr. Sil- 

 urian ; Prague (after Barrande). All figures 

 natural size. 



Fig. 211. 



Rastrites Knnaei Barr. Silurian ; Zekko- 

 witz, near Prague (after Barrande). 



are known also in South America (Bolivia), and Australia, and are not un- 

 common in the drift which Covers the plains of Northern Germany. 



According to Lapworth, Graptolites are distributed vertically throughout 

 six difFerent horizons ; 'the first of these coincides with the Upper Cambrian, 

 the three foUowing with the Ordovician, and the two uppermost with the 

 Silurian. The Monoprionidae are especially characteristic of the two Silurian 

 horizons. 



[The discussion of tlie group Graptolitoidea in the present work has been revised by Dr. 

 Rudolf Riiedemann, of the New York State Geological Survey, at Albany, New York. — 

 Editor. 1 



Subclass 2. ACALEPHAE Cuvier. Scyphomedusae.^ 



{Discophora Huxley). 



Free-swimming, discoidal or bell-shaped Medusae, with downwardly direded mouth, 

 with gastro-vascular pouches and numerous radial canalSj and having, as a rule, the 

 margin of the umhrella lobed. Cambrian to Eecent. 



The Acalephs or Lobed Jelly-fishes, though frequently of considerable 

 size, are entirely without hard parts, and therefore are unfitted for preservation 



^ Literature : Huxley, T., Memoir on the Anatomy and Affinities of the Medusae. Phil. Trans,, 

 1849. — K7ier, R., Ueber eine Meduse in Feuerstein. Sitzungsber. Akad. Wiss. Wien, 1865, vol. lii. — 

 Haeckel, E., Ueber fossile Medusen. Zeitschr. für Wissenschaft. Zool., 1865 and 1870, vols. xv., xvii. 

 Neues Jahrb. für Mineral., 1866. Jenaische Zeitschr., 1874, vol. viii. System der Medusen, i. and 

 ii., Jena, \^^0-^\.—Nathorst, A. G., Om Aftryck af Medusor, etc. K. Svenska Vetensk. Akad. 



