250 REPORT ON THE STATE CABINET. 



carbonaceous substance, have induced me to place this fossil among the 

 Graptolitid^B. 



There is still another form known, which may be doubtfully classed 

 among the Graptolitidge. It consists of a slender flexible median rachis, 

 on each side of which are placed, in alternating order, slender flattened 

 pinnulge, which are of nearly equal width throughout, and are themselves 

 flexuous. Upon one side of the rachis are minute points or dots, 

 which have apparently been the cell-apertures. The test is a black cor- 

 neous or carbonaceous substance, but there is no evidence of a solid 

 central axis. These bodies are numerous in some shaly beds of the age 

 of the Trenton limestone, at Plattville, Wisconsin. For these forms I 

 have proposed the name of Buthograptus.* 



Associated with the preceding forms there are some stipes of corneous 

 or carbonaceous texture, frequently branched, the branches again dividing, 

 and sometimes, if not always arranged in whorls; in one of which six 

 divisions were counted. The general form of the body is not unlike that 

 of Dendrograptus, but the branches are more slender, and ramify in a 

 different manner, while there are no visible cellules. In the absence of 

 farther knowledge, I refer these fossils, with hesitation, to the Genus 

 Oldhamia (0./rt(fecosa, Hall). 



The variety of form and mode of development among the Graptolites 

 is shown by the collections from the Quebec and Hudson river groups to 

 be much greater than had ever before been supposed. The number of 

 species which have been traced to their origin or initial point, and whose 

 mode of growth has been verified, is probably larger than in all collec- 

 tions heretofore made ; and, together with those before known, enables 

 us to give a very good exposition of the characters of this family of fossils. 



SYNOPSIS OP THE GENERA OP GRAPTOIiITID.ffl. 

 I. 



Polypary, with a single series of cells, cousistiiig of simple or divided stipes, 

 or of branching fronds with a bilateral an'angment of the parts; a solid axis 

 and common body. 



1. The successive buds developed in tubular cellules ijiydrotheca), 

 which are in contact for a greater or less portion of their length, 

 and inclined towards the axis.f 



* Report of Progress of the Geological Survey of Wisconsin for 1860, communicated January 

 1st, 1861. 



t This section as here presented is simply a revision of section 1 a of Report, p. 217, recogniz- 

 ing the genera which have been proposed for those forms heretofore placed under the genus 



GbAPTOLITHUS of LlNNiEUS. 



