216 TWENTIETH REPORT ON THE STATE CABINET. 



Graptolitidae as these appearances indicate, it may be found necessary to 

 separate them from this family. 



The Grenus Dictyonema is restricted to such forms as have the numerous 

 stipes and branches connected by transverse processes, and the whole 

 united in a flabelliform or funnel-shaped frond, without elongate stem or 

 trunk. The stipes and branches are irregularly striated externally, con- 

 sisting of a corneous envelope, as in ordinary graptolites ; but I have not 

 been able to determine clearly the existence of a solid axis. The cellules 

 are indicated by angular processes or cell-denticles on the inner side of the 

 branches, as shown in fig. 5 of Plate i. 



In the Grenus Rastrites> of Barrande, the distinguishing features are the 

 slender cylindrical stipes or branches, with distinct slender tubular cellules. 



The few species of Thamnograptus known, consist of cylindrical or 

 sub-cylindrical stipes, with slender elongate alternating pinnulae or branch- 

 lets. No evidence of cellules has been observed in any of the specimens. 



The peculiar forms for which I have proposed the name Ptilograptus^ 

 consist of branching stems, which, in all their divisions, are studded on 

 each side, in alternating order, with narrow pinnulae. These are some- 

 times extremely slender, or even capillary in their dimensions. In one 

 species I have detected elliptical spots upon one face of the pinnulsB 

 which are slightly flattened, and I infer that these are the cell-apertures. 

 The substance of the test is corneous, and there is an internal solid axis. 

 Although I have placed these forms under the Grraptolitidse with some 

 hesitation, the form of cellules may perhaps render a separation desirable ; 

 but with our present information, such a separation cannot at this time 

 be made. 



The Grenus Inocaulis was proposed for some flattened stipes with a sca- 

 brous surface, which have the appearance of denticles upon the margins. 

 These stipes grow in close groups or tufts, and are bifurcating or branched 

 in their upper portions. No positive evidence of cellules has been observed. 

 The presence of denticles, together with a corneous or carbonaceous sub- 

 stance, have induced me to place this fossil among the Graptolitidae. 



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

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

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

 pinnulae, 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 corneous 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 I have proposed the name 

 of Butkograptus.* 



* Report of Progress of the Geological Surrey of Wisconsin for 1860, p. 19; communi- 

 cated January 1st, 1861. 



