210 TWENTIETH REPORT ON THE STATE CABINET. 



branches," we may remark, that we have three or four species of the 

 four-stiped form, or '■'■ Tetr a gr opt us ^^ with the central corneous plate; 

 while we have four species which are not known to possess it. Of the two 

 eight-stiped species known, one has the central corneous plate or disc, and 

 the other was probably destitute of such an appendage. In G. logani, 

 with its numerous simple stipes, the central corneou** plate is usually 

 present, though not in all examples ; while G. multifasciatus, with more 

 numerous simple stipes than G. logani, is not known to have a central 

 corneous disc, and, from its mode of growth, probably never possessed 

 such an appendage. From the irregularity of growth in the G. ab7iormis, 

 I infer that there was no central plate. 



In all the properly-branching species where the initial point is known, 

 as in G.Jiexilis, G. rigidus, and G. milesi, no such central plate has ever 

 been seen ; nor h;is it been shown in any European species, so far as I 

 know. Those with the " fronds repeatedly dichotomous,'' similar to the 

 one originally proposed by Mr. Salter * as the type of Dichograptus, are 

 not known to possess the central corneous disc. 



Although entirely willing to accept and adopt such subdivisions of the 

 graptolites as will aid in determining their zoolog-ical character and 

 relations, their geological value, or indications of differences in mode of 

 development, I do not appreciate the force and value of these proposed 

 generic subdivisions for the two, foui* and eight-stiped species, or the 

 presence or absence of a central corneous disc as indicating generic distinc- 

 tions ; since it is impossible to obtain any aid from such designations 

 for the references of the numerous fragments which are the ordinary form 

 and condition in which we find the graptolites, and in which they must 

 generally be studied. 



The form, mode of growth, and arrangement of cellules in all these 

 several proposed genera, are so identical in plan as to afford no means for 

 generic separation ; and although the same is true of the properly ramose 

 forms, yet I conceive it might have been convenient to adopt a term 

 {Dichograptus or Cladograptus) indicating the ramose character of the 

 stipes, regarding as true branches only the subdivisions which take place 

 after the commencement of the cellules. 



The Genus Nereograpcusj of GtEINITZ, proposed by that author to include 

 such forms as Nereites, Myrianites, and Nemei'tites of Murchison, and 

 Nemapodia of Emmons, etc., can scarcely be admitted into the family of 

 G-raptolitidae, since all the American species referred to the first three 

 named genera have no texture or structure like graptolites, and (as I have 

 elsewhere shown) appear to be referable to the tracks or trails of some 

 marine worms or other animals upon the sea-bottom ; while Nemapodia is 



* Geologist, Vol. 4, p. 74, 1861. 



f Nereograpsus: Die Verstein. Grauwacken formation, etc., Graptolithen, p. 27. 



