114 



COELENTERATA CNIDARIA 



CLASS II 



individual polyps. The proliferous zooids are developed within urn-shaped capsules 

 (gonothecae) of comparatively large size, and sometimes become separated off us 

 free-swimming velate Medusae. 



Although existing Campanularians (Sertularidae, Plumularidae, Campanu- 

 Jaridae) are provided with a durable periderm, their remains have not as yet 

 been detected in the fossil state, with the exception of a few forms from the 

 Pleistocene. Nevertheless, in the Upper Cambrian, Ordovician, Silurian, and 



occasionally in the Devonian, numerous 

 finely branching plant -like remains are 

 found, which are sometimes furnished with 

 a strong foot-stalk, and sometimes terminate 

 acutely at the base ; the original substance 

 of which was undoubtedly chitinous. These 

 forms are grouped together under the 

 common term Cladophora, Hopkinson, and 

 may be regarded as- early types of the Cam- 

 panulariae. Particularly well - preserved 

 specimens exhibit on one or occasionally on 

 both sides of the branchlets small cellules 

 or hydrothecae, which evidently served for 

 the reception of zooids. Very often the 

 branches are united by numerous slender 

 transverse processes or dissepiments. 



In the genera Dendrograptus, Callograptus, 

 Thamnogmptus, and Inocaulis, Hall ; Calypto- 

 . Hal1 - Silurian qraptus. Spencer ; Brwqraptus. Lapworth, 



(Niagara) ; Lockport, New York. Natural size. y * ' y y ^ ' " . 



b, Dictyo-nema, sp. Branch-bearing hydrothecae. etc., the Organisms are provided With a 



> thick foot-stalk, by which they were prob- 

 ably attached to some foreign object. The branches are numerous, slender, 

 often bifurcating, bear hydrothecae, and are connected by transverse processes. 

 Dictyonema, Hall (Dictyograptus, Hopkin.), (Fig. 201). Funnel- or fan-sTiaped 

 branching fronds terminating acutely .at the base, and probably unattached. 

 Branches united at short intervals by dissepiments, and furnished distally on 

 one side with hydrothecae ; the latter, however, are rarely well preserved. 

 Ordovician to . Devonian. Particularly common in Ordovician rocks near 

 Christiania, Norway, but usually compressed into fan-like networks. 



Appendix to the Campanulariae. 



Graptolitoidea, Lapworth (Bhabdopkora, Allman). 1 



Under the term Graptolitoidea or Graptolites are included organisms which 

 are generally found accompanying the Cladophora in Palaeozoic strata, and 



1 Barrande, J., Graptolites de Bohenie. Prague, 1850. Geinitz, 11. B., Die Versteinerungen 

 der Grauwackenformation in Sachsen. Leipsic, 1852. Die Graptolithen des mineral ogischen 

 Museums in Dresden, 1890. Hall, /"., Graptolites of the Quebec. Group. Canadian Organic Remains, 

 Decade II. (Geol. Surv. Canada), 1865. Herrmann, 0., Die Graptolithen-Familie Dichograptidae, 

 1885. Holm, G., Gotlands Graptoliter (Bihang Svenska Vetensk. Ak. Handl. vol. XVI.), 1890. 

 On Didymograptus, Tetragraptus, etc. (Geol. Fdren. Stockholm Forhandl. XVII.), 1895. Lapworth, 

 C., Notes on the British Graptolites (Geol. Mag. vols. X. and XIII.), 1873-76. Also various papers 



