I\i/c'()iito/ogy of the Ciiiciiinati Croup. 151 



polypites united by a coniinon stem or "cceuosarc;" outer 

 covering chitinous or corneous, investing the crcnosarc, and 

 prolonged into hydrothecie. 



To this order two genera, generally classed under Grapto- 

 lites, are referred by Nicholson. They are Dendrograpius 

 and Dictyoncnm, and are readily distinguished from each 

 other. In the first the stem is branching and plant-like ; in 

 the second it forms a reticulated net-work. The two genera 

 differ mainly from the true Graptolites by having a base for 

 attachment, tlic typical Oraptolitoidea lacking this.-'' 



Genus i. — Dendrograptus, Hall, 1862. 



Fronds simple or aggregate, consisting of a strong foot- 

 stalk, sometimes furnished below with a distinct root, or 

 root-like bulb, and above variously ramified and divided into 

 numerous branches and branchlets, slightly divergent-; the 

 whole thus appears shrub-like ; fronds some times flabellate 

 (?) ; branches celluliferous on one side ; cellules appearing 

 sometimes as simple indentations on the surface, sometimes 

 distincth' angular, with conspicuous denticles ; substance of 

 stipe and branches corneous ; solid or tubular ; surface 

 striated ; the denticles are sometimes absent from some 

 branches. (Hall, Geol. of Wisconsin, vol. i, 1862, name 

 onl)-, p. 21. Grap. of Quebec Group. Can. Organic Remains, 

 Decade H, 1865, p. 126; Nicholson, Mon. of Brit. Graptolitidse, 

 pt. I, 1872, p. 127. Biithotrcphis in part. Psilophyton in part.) 



Remarks — This genus was first proposed in the Geology of 

 Wisconsin, as noted above, but it does not seem to have been 

 described until 1865, when the "Graptolites of the Quebec 

 Group" was published. It is probable that the species de- 

 scribed by Hall as Buthotrcphis gracilis is really a graptolite, 

 and there is no doubt in the mind of the writer that Psilophy- 

 ton graci/IiiiiNDi, Lesqx., is really one. 



I. I). GRACiLiJMUM, Lesqx. (sp.) 1877. 



"Stem very slender, dichotomoush' branched, smooth or 

 naked half round, slightly channeled in the length, branches 

 numerous, of various length, filiform." (Am. Phil. Soc, 



*Kor numerous references and notes in the portion which fonovvs I am indebted 

 to Dr. R. R. Gurley, of the U. S. Fish Commission. He has been engaged for sev- 

 eral years past in the study of the group of GraptoHtes. 



