No. 186.] 49 



fragments found. Moreover there are such various modes of branch- 

 ing, that such forms as G. ramosus present but little analogy with 

 such as G. gracilis. 



M. Geinitz introduces among the Graptolitidece the genus JYereo- 

 grapsus^ to include JYereites, Myrianites^ JYemertites and JVemapodia. 

 Admitting the first three of these to be organic remains, which the 

 writer has elsewhere expressed his reasons for doubting, they are 

 not related in structure, substance, or mode of occurrence, to the 

 Graptolites, at least so far as regards American species; and the 

 JVemapodia is not a fossil body, nor the imprint of one, but simply 

 the recent track of a slug over the surface of the slates. The genus 

 Rastrites of Barrande has not yet been recognized among American 

 GraptolitidecB. These forms are by Geinitz united to his genus 

 Cladograpsus, the propriety of which we are unable to decide. 



The genus Gladiolites ( Retiolites of Barrande, 1850 ; Grapto- 

 phyllia of Hall, 1849) occurs among American forms of the Gra- 

 ptolitidecB in a single species in the Clinton group of New- York. A 

 form analogous, with the reticulated margins and straight midrib, 

 has been obtained from the shales of the Hudson-river group in 

 Canada; suggesting an inquiry as to whether the separation of this 

 genus, on account of the reticulated structure alone, can be sus- 

 tained. In the mean time we may add that the Canada collection 

 sustains the opinion already expressed, that the Bictyonema will 

 form a genus of the family Graptolitideee. The same collection has 

 brought to light other specimens of a character so unlike anything 

 heretofore described, that another very distinct genus will thereby 

 be added to this family. The Canadian specimens show that the 

 Graptolites are far from always being simple or merely branching 

 flattened stems. 



The following diagnosis will express more accurately the character 

 of the Genus Graptolithus, as ascertained from an examination of 

 perfect specimens in this collection. 



Genus Graptolithus (Linnaeus). 



Corallum or bryozoum fixed (free?), simple or compound; the parts bi- 

 laterally arranged, consisting of simple stipes or of few or many simple 

 or variously bifurcating branches, radiating more or less regularly from 

 a centre, and, in the compound forms, united towards their base in a 

 continuous thin corneous membrane or disk formed by an expansion of 

 the substance of the branches, and which in the living state may have 

 been in some degree gelatinous. Branches with a single or double series 

 of cellules or serratures, communicating with a common longitudinal 

 [Assembly No. 186.J 7 



